Risk Analysis for 

Phytophthora ramorum Werres, de Cock & Man in't Veld, 

Causal Agent of Sudden Oak Death, 

Ramorum Leaf Blight, and Ramorum Dieback 

Gary L. Cave, Ph.D., Entomologist 

Betsy Randall-Schadel, Ph.D., Plant Pathologist 

Scott C. Redlin, Ph.D., Plant Pathologist 

United States Department of Agriculture 

Animal and Plant Health Inspection Service 

Plant Protection and Quarantine 

Center for Plant Health Science and Technology 

Plant Epidemiology and Risk Analysis Laboratory 

1730 Varsity Drive, Suite 300 

Raleigh, NC 27606 

 Revision 1 

January 25, 2008 
 

Executive Summary 

This pest risk analysis was conducted by the United States Department of Agriculture, Animal 

and Plant Health Inspection Service, Plant Protection and Quarantine, Center for Plant Health 

Science and Technology, Plant Epidemiology and Risk Analysis Laboratory to assess the risk of 

the importation and domestic spread of Phytophthora ramorum Werres, de Cock, & Man in’t 

Veld, 2001. This pathogen is the subject of USDA Emergency Regulations due to its threat to 

agricultural, horticultural, and natural ecosystems in the United States. The analysis focused on 

1) the risks associated with the importation of plants (including plants in APHIS-approved 

growing media and bare-root plants) and plant products (wood, lumber, chips, bark and other 

wood products, and greenery) that are hosts of P. ramorum; 2) the risks associated with the 

domestic movement of the pathogen through plants, plant products, soil, other growing media, 

compost, and water; and 3) mitigation measures to prevent the movement and spread of P. 

ramorum to non-infested areas in the United States. 

Diseases caused by an unknown species of Phytophthora were first observed in Europe on 

nursery stock in 1993 and in California forests on Quercus spp. and Lithocarpus densiflorus in 

1995, but the pathogen, P. ramorum, was not formally described until 2001. Since initial reports 

and detections, P. ramorum has expanded its geographic distribution in forested areas of 

California and Oregon and has been detected in hundreds of nurseries in Europe and North 

America. The pathogen continues to be detected on new hosts and in nurseries outside of 

quarantined and regulated areas. 

Several biological factors affect the risk of introduction and establishment of P. ramorum, 

including the large host range, variation in symptoms, production of multiple spore states, and 

factors inducing and breaking latency and dormancy. The large host range is mirrored by the 

complexity of the disease symptoms, which can be grouped into three general disease categories: 

canker, foliage, and dieback. Hosts can exhibit the symptoms of one or more of these disease 

categories. 

The risk presented by P. ramorum is High. The risk is based on six Elements: Climate-Host 

Interaction, Host Range, Dispersal Potential, Economic Impact, Environmental Impact, and Pest 

Opportunity. 

Climate-Host Interaction. The risk rating is High for this element. The level of certainty for 

this risk rating is fairly certain. Most of the eastern United States has actual and potential hosts 

growing in climates conducive to infection. The uncertainty lies in the range of biotic and 

abiotic factors triggering the establishment of P. ramorum in new areas. 

Host Range. The large number of hosts in multiple plant families, differential susceptibility, 

and virulence warrant a High risk rating. The level of uncertainty of this risk element is low 

because P. ramorum already has a large demonstrated host range. 

Dispersal Potential. In the United States, both regulated and associated hosts are widely 

distributed, overlapping, abundant, and susceptible. In addition, the pathogen is polycyclic, 

infections may remain undetected for years, long-distance dispersal via trade has been 
demonstrated, and circumstantial evidence suggests spread by natural means. For these reasons, 

the risk rating for this element is High and the level of uncertainty is Low based on the evidence 

of human-assisted and natural movement. 

Economic Impact. Phytophthora ramorum is impacting the international and domestic 

movement of plants and plant products (nursery stock, fruit, logs, lumber, etc.) and has resulted 

in restrictions in trade and movement. The risk rating for this element is High and the 

uncertainty depends on the relationships between the extent of the host range and the value of 

these plants on the open market. 

Environmental Impact. The risk rating for this element is High. The environmental factors 

include: (1) direct costs of prevention, eradication, or suppression, (2) current-use and future-use 

values, and (3) indirect ecological consequences (changes in locally important ecological 

processes such as perturbations of hydrological cycles, e.g., flood control and water supply; 

waste assimilation; nutrient recycling, conservation, and regeneration of soils; and crop 

pollination). Assessing the environmental impact is difficult due to the uncertainty of cost 

estimates that address all of the relevant ecological components; therefore, the uncertainty of this 

element is High. 

Pest Opportunity for Introduction. The rating for Likelihood of Introduction is High. Both 

natural and human-assisted factors aid in the dispersal of P. ramorum to areas where suitable 

hosts and climatic conditions are conducive to establishing and sustaining a population. 

Differences in reproductive ability and infection susceptibility of a large number of hosts 

contribute to the uncertainty. The uncertainty for this rating is High and is based on the 

variability in detecting P. ramorum and the ability to predict the levels of resistance and 

susceptibility among hosts and potential hosts occurring in non-infested regions. 

In addition, the following pathways were analyzed: nursery stock, Christmas trees (cut and 

living), cut foliage/flowers, wood and wood products, greenwaste and compost, potting media, 

and soil. Although individual elements for cut Christmas trees and cut foliage/flowers pathways 

were rated Medium, the overall risk potential for all pathways was High. 

Current regulatory efforts (exclusion, eradication, containment, suppression, and sanitation) and 

potential mitigations for pathways were reviewed. There are considerable challenges in 

devitalizing this pathogen because it occurs in forests and regulated articles (e.g. nursery stock, 

wood/wood products, compost). In addition, there are a limited number of long-term fungicidal 

or eradicant treatments and the efficacy of these treatments to inoculum varies. 

Exclusion is the most effective mitigation option, but domestic and international trade render this 

difficult. Eradication of the pathogen via chemicals is problematic, because the pesticides 

available for control are fungistatic, not fungicidal. Containment and suppression efforts vary 

based on forest and nursery scenarios. These include forest and water surveys, nursery 

certification programs, and other methods to reduce inoculum, such as the destruction of host 

material. Sanitation (pathogen-free water, pots, potting media, benches, tools and equipment, 

clothing, etc.) is required to maintain pathogen-free material. 
Pathway mitigation measures include chemical, physical, and cultural and biological treatments. 

The efficacy of chemical control is dependent upon timing, type of application, and location of 

the pathogen in or on the plant. Physical control includes heat, heat and vacuum, heat via aerated 

steam, removal of infected bark and wood, and air drying. Cultural and biological methods 

include best management practices and the use of biological antagonists. 
Table of Contents 

I. Initiating Event: Proposed Action .............................................................................................. 1 

II. Glossary..................................................................................................................................... 2 

III. Pest Data Sheet ........................................................................................................................ 4 

A. Identity .................................................................................................................................. 4 

B. Hosts...................................................................................................................................... 4 

C. Geographic Distribution...................................................................................................... 10 

D. Biology and Epidemiology ................................................................................................. 11 

E. Detection and Identification ................................................................................................ 14 

IV. Organism Risk Assessment ................................................................................................... 18 

A. Prior Risk Assessments, Current Status, and Interceptions ................................................ 18 

B. Consequences of Introduction............................................................................................. 19 

C. Likelihood of Introduction .................................................................................................. 26 

D. Pest Risk Potential .............................................................................................................. 28 

V. Pathway Assessments ............................................................................................................. 31 

A. Consequences of Introduction............................................................................................. 31 

B. Likelihood of Introduction to New Areas in the United States........................................... 40 

C. Pest Risk Potential............................................................................................................... 45 

VI. Mitigation Measures .............................................................................................................. 46 

A. Introduction......................................................................................................................... 46 

B. Regulatory Measures........................................................................................................... 47 

C. Nursery Stock, Christmas Trees, and Cut Foliage/Flowers ................................................ 51 

D. Wood and Wood Products .................................................................................................. 53 

E. Greenwaste and Compost.................................................................................................... 55 

F. Potting Media and Soil ........................................................................................................ 55 

VII. Acknowledgements ............................................................................................................. 61 

VIII. Literature Cited ................................................................................................................... 62 
List of Tables and Figures 

Table 1. Proven Hosts and Plants Associated with Phytophthora ramorum as listed by the United 

States Department of Agriculture as of December 1, 2007 coupled with the disease(s) and 

affected plant part(s) ................................................................................................................. 6 

Table 2. Plant genera with detections of Phytophthora ramorum in Europe. ............................. 10 

Table 3. Summary of characteristics of the three lineages of Phytophthora ramorum. ............... 12 

Table 4 Summary of USDA funding for Phytophthora ramorum............................................... 25 

Table 5. Imports of plant materials from Europe and Canada to the United States (quantity in 

1000 units; value in $1000 U.S.) ............................................................................................ 29 

Table 6. Comparative risk matrix for Phytophthora ramorum assessment and selected unmitigated 

pathways................................................................................................................................... 46 

Table 7. Fungicides labeled for control of Phytophthora diseases.............................................. 50 

Fig. 1. Possible disease cycle for sudden oak death, ramorum leaf blight and ramorum 

dieback .................................................................................................................................... 17 

Fig. 2. Overall risk index for the establishment of Phytophthora ramorum in the continental 

United States based on introduction potential, climate potential, economic potential, and host 

strength.................................................................................................................................... 24 

Fig. 3. Locations receiving plants shipped from nurseries testing positive for Phytophthora 

ramorum 2004-2006 overlaid on climate potential ................................................................ 30 

Fig. 4. Potential points for the application of mitigation measures for the foliar host phase are 

indicated with shears............................................................................................................... 57 

Fig. 5. Potential points for the application of mitigation measures for the canker host phase are 

indicated with shears............................................................................................................... 58 

Fig. 6. Potential points for the application of mitigation measures for the soil phase are indicated 

with shears .............................................................................................................................. 59 

Fig. 7. Potential points for the application of mitigation measures for the survival/dormancy 

phase are indicated with shears............................................................................................... 60 
I. Initiating Event: Proposed Action 

This is an update of the pest risk analysis (PRA) conducted in May 2005 by the United States 

Department of Agriculture, Animal and Plant Health Inspection Service, Plant Protection and 

Quarantine, Center for Plant Health Science and Technology, Plant Epidemiology and Risk 

Analysis Laboratory (USDA, APHIS, PPQ, CPHST, PERAL) to assess the risk of the 

importation and domestic spread of Phytophthora ramorum Werres, de Cock, & Man in’t Veld, 

2001. Phytophthora ramorum is the subject of USDA Emergency Regulations due to its threat to 

agricultural and natural ecosystems in the United States. This analysis will focus on 1) the risks 

associated with the importation of plants (including plants in APHIS-approved growing media 

and bare-root plants) and plant products (wood, lumber, chips, bark and other wood products, 

and greenery) of hosts of P. ramorum; 2) the risks associated with the domestic movement of the 

pathogen through plants, plant products, soil, other growing media, compost, and water; and 3) 

mitigation measures to prevent the movement and spread of P. ramorum to non-infested areas in 

the United States. This document consists of four major components: a pest data sheet, an 

organism assessment, pathway assessments, and mitigation measures. The pathways analyzed 

are nursery stock, Christmas trees, cut foliage/flowers, wood and wood products, greenwaste and 

compost, potting media, and soil. 

The authority for APHIS to regulate plant pests and plant products is derived from the Plant 

Protection Act of 2000 (7 USC §7701 et seq.); for plant imports, the Nursery Stock, Plants, 

Roots, Bulbs, Seed and Other Plant Products subpart of the Code of Federal Regulations (7 CFR 

§319.37); and for regulating domestic interstate movement of items at risk for moving 

P. ramorum, Phytophthora Ramorum (7 CFR §301.92). The risk assessment methodology and 

rating criteria (APHIS, 2002) and the use of biological and phytosanitary terms are consistent 

with relevant international standards published by the International Plant Protection Convention 

(IPPC). 

The current pest risk analysis was prepared in response to a need to promulgate regulations 

addressing the international and domestic movement of P. ramorum and its hosts at the genus 

level. The justification for this approach is based on scientific considerations such as an 

expanding list of natural hosts (22 families, 42 genera, and over 66 species reported as natural 

hosts in 2005; 35 families, 70 genera, and over 109 species in 2007), the unknown host 

specificity of this pathogen, the potential movement of infected asymptomatic plants, the 

variability of environmental conditions leading to expression of the disease, the expanding list of 

countries reporting the pathogen (seven European countries reported detections in 2005; 16 

countries reported detections in 2007), and recent expansions within the United States, 

specifically in Humboldt County, CA and Curry County, OR. A compounding problem is the 

variable resistance observed within a species, e.g., Umbellularia californica (Meshriy et al., 

2005). Additionally, although hosts may be present in different countries, they have not been 

found to be infected in all counties, even when the pathogen is present; for example, Quercus 

rubra is present in the United Kingdom (Jones et al., 2003) and the Netherlands, but only found 

infected in the Netherlands (RAPRA, 2007). The analysis addresses the potential risks from 

products associated with these host genera, including soil, compost, and growing media 

1 
The domestic movement of P. ramorum is currently regulated under an Interim Rule, “Domestic 

Quarantine Notices Phytophthora Ramorum” 7 CFR §301.92, and an Agriculture Department 

Emergency Federal Order Restricting Movement of Nursery Stock from California, Oregon, and 

Washington Nurseries (APHIS, 2007b). The USDA implemented emergency measures to 

regulate the international movement of regulated articles from Europe; these measures mirrored 

the federal domestic regulations that went into effect November 1, 2002. Changes in Federal 

domestic emergency measures are applied to movement from Europe (February 27, 2007). 

II. Glossary 

The majority of the terms listed are quoted directly from the reference cited. 

Baiting – A method of recovering fungi from aquatic and soil/potting media by using various 

types of organic substrates. Classic baiting techniques for species of Phytophthora (Erwin and 

Ribeiro, 1996) using pears and leaves of hosts are used for P. ramorum (APHIS, 2004b). 

Chlamydospore – Spore, usually globose but occasionally ovoid, that is delimited from the 

mycelium by a septum and may be terminal (at the end of the hyphae) or intercalary (formed in 

the middle of a hyphal strand) with a thickened wall. It “...survives for a long time in soil” 

(Erwin and Ribeiro, 1996). 

Disease Cycle – This is the sequence of events involved in disease development, including the 

stages of development of the pathogen and the effect of the disease on the host; the chain of 

events that occurs between the time of infection and the final expression of disease (Shurtleff and 

Averre, 1997). 

Heterothallism (adjective heterothallic) – Self-sterility; a sexual condition in which an 

individual produces only one kind of gamete. Used chiefly in reference to fungi and algae 

(Shurtleff and Averre, 1997). 

Host – A living organism (e.g., a plant) harboring or invaded by a parasite and from which the 

parasite obtains part or all of its nourishment (Shurtleff and Averre, 1997). 

Regulated Host – Host plant that is naturally infected and for which Koch’s postulates 

have been completed, documented, reviewed, and accepted. Some are regulated in part 

(such as redwood and Douglas-fir) and some are regulated in their entirety (such as 

tanoak and western starflower) (APHIS, 2007a). 

Associated Plant – Host plant that is reported to be naturally infected and from which P. 

ramorum has been cultured and/or detected using polymerase chain reaction (PCR). For 

each of these, traditional Koch’s postulates have not yet been completed or documented 

and reviewed. These reports must be documented and reviewed by PPQ before a plant 

becomes an APHIS Regulated Host for P. ramorum (APHIS, 2007a). 

Experimental Host – Host plant that has indicated susceptibility to infection by 

P. ramorum in experiments. 

Host Range – The complete range of plants that may be attacked by a given pathogen (Shurtleff 

and Averre, 1997). 

Hypha(e) – The basic vegetative unit of structure and function of most fungi; a largely 

microscopic tubular filament that increases in length by growth at its tip. New hyphae arise as 

lateral branches. Some can become specialized for given functions including producing spores, 

penetrating host tissues, etc. (Erwin and Ribeiro, 1996). 

2 
Koch’s Postulates – Four rules, proposed by Robert Koch, followed to prove the pathogenicity 

of a microorganism (Shurtleff and Averre, 1997). The rules below work well for most fungi, 

bacteria, nematodes, and related organisms (Agrios, 2005). A modification is used for hard to 

isolate pathogens, such as some viruses (Agrios, 2005, p. 27; Shurtleff and Averre, 1997). 

Rule 1. Organism is consistently associated with a disease syndrome. 

Rule 2. Organism is isolated and grown in pure culture. 

Rule 3. Organism is used to inoculate a healthy host of the same species and the same 

disease syndrome noted in rule 1 is observed. 

Rule 4. Organism is re-isolated from the inoculated plant and has the same 

characteristics as the initial isolate (Shurtleff and Averre, 1997). 

If all of the above steps...are followed and proved true, then the isolated pathogen is identified as 

the organism responsible for the disease (Agrios, 1997, p. 40). 

Latent Infection – Infection in a plant without visual symptoms (Shurtleff and Averre, 1997). 

See Latency. 

Latency – Stage of an infectious disease, other than the incubation period, where no symptoms 

are expressed in the host (Shurtleff and Averre, 1997). 

Life Cycle – Cyclical progression of stages in the growth and development of an organism 

(plant, animal, or pathogen) that occur between the appearance and reappearance of the same 

stage of the organism (Shurtleff and Averre, 1997). 

Mating Types – Compatible strains, usually designated + and – or A and B, necessary for sexual 

reproduction in heterothallic fungi (Shurtleff and Averre, 1997). 

Monocyclic – Having one cycle per growing season; no secondary infections (Shurtleff and 

Averre, 1997). 

Mycelium – Tubular strands that make up the body of the fungal microorganism. In 

Phytophthora, mycelium is non-septate, but plugs, often called false septa, can be seen in old 

mycelium (Erwin and Ribeiro, 1996). 

Oomycete(s) (Oomycota, Peronosporomycetes, Chromista) – A class of the Mastigomycotina, 

typically aquatic, saprobic, or parasitic fungi that produce oogonia, antheridia, and oospores 

(Shurtleff and Averre, 1997). A fungus-like chromistan that produces oospores; a water mold 

(Agrios, 2005, p. 895). These organisms are now classified as Peronosporomycetes and placed 

within the Straminipila (Abad, 2007; Dick, 2001; Dick et al., 1984). 

Oospore – Thick-walled, resting spore in the oomycetes that develops from a fertilized oosphere 

or by parthenogenesis (Shurtleff and Averre, 1997). 

Pest Risk Analysis – The process of evaluating biological or other scientific and economic 

evidence to determine whether a pest should be regulated and the strength of any phytosanitary 

measures to be taken against it (IPPC, 2002). 

Pest Risk Assessment – Determination of whether a pest is a quarantine pest and evaluation of 

its introduction potential (IPPC, 2002). 

Pest Risk Management – The decision-making process of reducing the risk of introduction of a 

quarantine pest (IPPC, 2002). 

Polycyclic – A disease of which many cycles occur in one growing season, resulting in many 

secondary infections (Shurtleff and Averre, 1997). 

3 
 

Propagule – Any part of an organism capable of initiating independent growth when separated 

from the parent body (Shurtleff and Averre, 1997). In the case of P. ramorum, propagules 

reported from nature are mycelia, sporangia, chlamydospores, and zoospores. Oospores have 

been produced in the laboratory. 

Soil –The loose surface material of the earth in which plants grow, in most cases consisting of 

disintegrated rock with an admixture of organic material (NAPPO, 2004). 

Sporangium/sporangia – Sac within which zoospores form, especially when water is cooled to 

about 10°C below ambient temperature. In solid substrates, sporangia usually germinate by 

germ tubes (Erwin and Ribeiro, 1996). 

Sporulate, Sporulation – To form or produce spores (Shurtleff and Averre, 1997). 

Zoospore – Spore that forms within the sporangium and exits through the terminal pore, has a 

tinsel and a whiplash flagellum, and is capable of swimming for several hours (Erwin and 

Ribeiro, 1996). 

III. Pest Data Sheet 

A. Identity 

Name: Phytophthora ramorum Werres, de Cock, & Man in’t Veld (2001) 

Synonym: none 

Taxonomic position: Straminipila: Peronosporomycetes (Oomycetes): Pythiales: Pythiaceae: 

Phytophthora (Dick, 2001; Dick et al., 1984) 

Disease names: Sudden oak death (Ramorum bleeding canker in the United Kingdom), 

Ramorum leaf blight, Ramorum twig blight or dieback 

B. Hosts 

The host range (Table 1) for Phytophthora ramorum is broad and continues to expand. As of 

December 1, 2007, 40 plant species and all the species in five genera are designated as proven 

hosts, with an additional 65 species listed as associated plants by USDA (APHIS, 2007a). The 

difference between proven hosts and associated plants is a successful demonstration of Koch’s 

Postulates (see Glossary). 

Proven Hosts: These hosts are regulated because Koch’s Postulates have been demonstrated, 

documented, and reviewed. The parts of the host that are regulated depend on the tissues 

infected by the pathogen. Damage to the timber, tourism, and nursery industries, and the 

environment has been documented (Davidson et al., 2003b). Details for selected hosts are listed 

below. 

Caprifoliaceae: The Caprifoliaceae includes important nursery and landscape species worldwide, 

particularly the genus Viburnum. One of the first hosts detected in Europe was Viburnum x 

bodnantense (Werres et al., 2001). Lane et al. (2003) reported the first infection of V. tinus by 

P. ramorum. Plants displayed severe aerial dieback, stem base discoloration, and partial root 

decay. Flower blight has also been reported (DEFRA, 2006). 

Ericaceae: This family encompasses another important group of nursery and landscape plants, 

e.g., Kalmia spp., Pieris spp., and Rhododendron spp. (Tooley et al., 2004). In addition, 

4 
members of this family are important environmental, wildland, understory, and small fruit 

production plants, e.g., Calluna vulgaris, Kalmia latifolia, Rhododendron spp., and Vaccinium 

spp., respectively. 

Fagaceae: This family includes a variety of forest species. Members of the red/black oak group 

section Lobatae, Quercus agrifolia, Q. parvula var. shrevei, and Q. kelloggii (Rizzo et al., 2002a, 

b), although not major timber species, are important to the environment and tourism. The 

red/black oak group includes several important timber species on the east coast, Q. rubra and Q. 

falcata (Table 1), which have both been found naturally infected in Europe (Brasier et al., 2004c; 

RAPRA, 2007). Q. chrysolepis, a member of section Protobalanus, is also a natural host 

(Davidson et al., 2003a, 2003b; Murphy and Rizzo, 2003). Three species of the white oak group 

(section Quercus) have been found to be susceptible: Q. ilex (naturally infected), Q. alba, and Q. 

robur (experimental hosts) (Brasier et al., 2002; Jones et al., 2003; Tooley and Kyde, 2007). 

Quercus cerris, a member of section Cerris native to Europe, Asia, and Africa, is a natural host 

of P. ramorum (RAPRA, 2007). Another member of the Fagaceae, Lithocarpus densiflorus, is 

unique in that its stems (trunks), twigs, and foliage are susceptible. This species is very common 

in northern California and southern Oregon (Barrett, 2006) and is important for wildlife food and 

habitat (Barrett et al., 2006). 

Pinaceae/Taxodiaceae: Forest trees include important timber species, e.g., Sequoia sempervirens 

(Taxodiaceae) and Pseudotsuga menziesii (Pinaceae). Only needles and twigs are regulated 

because infection in the field is limited to succulent growth (Chastagner et al., 2004, 2006b; 

Davidson et al., 2002a; Goheen et al., 2006b; Maloney et al., 2002a, b). Additionally, species 

used as Christmas trees or nursery stock, e.g. P. menziesii var. menziesii, are regulated for 

interstate movement (APHIS, 2007a, b). 

Lauraceae: Umbellularia californica can be an important source of inoculum. Occurrence of 

U. californica is highly correlated with sudden oak death incidence in Quercus and Lithocarpus 

in California (Kelly and Meentemeyer, 2002; Meshriy et al., 2005; Swiecki and Bernhardt, 

2002a, b), but not in Oregon (Hansen et al., 2005). Variation in susceptibility of 

P. ramorum has been observed in populations of U. californica (Meshriy et al., 2006). 

Theaceae: This family includes Camellia spp., which are important nursery and landscape 

plants. Camellia is regulated at the genus level because of the large number of species and 

hybrids determined to be hosts (APHIS, 2007b; Beales et al., 2004a; Parke et al., 2004a; 

Shishkoff, 2006). Phytophthora ramorum-infected Camellia plants have been detected in 

domestic and international trade (Bulluck et al., 2006; RAPRA, 2007). Linderman and Davis 

(2007a) demonstrated that although there were variations in lesion size and sporulation among 

cultivars of Camellia, all cultivars tested were susceptible. 

Associated Plants: Species symptomatic in a natural setting from which P. ramorum has been 

isolated but for which Koch’s postulates have not been demonstrated, documented, and reviewed 

are designated as Associated Plants (Table 1). Taxa are moved from the Associated Plant List to 

the Proven Host List when Koch’s Postulates are demonstrated and reviewed (APHIS, 2007a). 

Details for selected host families are listed below. 

5 
 

 

Oleaceae: This family contains important horticultural plants. Associated plant species in this 

family found naturally infected, are Fraxinus latifolia, Osmanthus decorus, O. delavaya, 

O. fragrans, and O. heterophyllus. All are foliar and shoot dieback hosts (RAPRA, 2007). 

Magnoliaceae: Members of this family are important ornamental and forest plants. 

Manglietia insignis, Magnolia grandiflora, M. maudiae, M. stellata, M. ernestii, Magnolia x 

loebneri, Magnolia x soulangeana, and Parakmeria lotungensis are primarily foliar hosts. 

Experimental Hosts: A database of experimental hosts is currently available on the Risk 

Analysis for P. ramorum website (RAPRA, 2007). Pathogenicity tests have been conducted by 

inoculating intact leaves, detached leaves, or both (Garbelotto et al., 2003; Parke et al., 2002b, 

2002c, 2006a; Tooley et al., 2004), log sections (Brasier et al., 2002; Hansen et al., 2005), and 

saplings (Rizzo et al., 2002b; Tooley and Kyde, 2007), and by infested media (Parke et al., 

2006b). These screening techniques are used to predict potential hosts (Parke et al., 2006a), but 

unless hosts are found naturally infected they will not be added to the Proven Hosts or 

Associated Plants List. 

Table 1. Proven Hosts and Plants Associated with Phytophthora ramorum as listed by the United States 

Department of Agriculture as of December 1, 20071 coupled with the disease(s) and affected plant part(s). 

Scientific Name Common Name Disease(s) Plant Part(s) 

Infected 

Proven Hosts 

Aceraceae 

Acer macrophyllum Bigleaf maple Leaf blight Leaf 

Acer pseudoplatanus Planetree maple Canker Trunk 

Caprifoliaceae 

Lonicera hispidula California honeysuckle Leaf blight Leaf 

Viburnum spp. Viburnum Canker Stem, Flower 

Ericaceae 

Arbutus menziesii Madrone Leaf blight, Dieback Branch, Leaf 

Arctostaphylos 

manzanita Manzanita Leaf blight, Canker Stem, Leaf, Twig, Branch 

Calluna vulgaris Heath Dieback Twig 

Kalmia spp. Mountain laurel Leaf blight, Dieback Leaf, Twig 

Pieris spp. Andromeda, Pieris Leaf blight, Dieback Leaf, Twig 

Rhododendron spp. Rhododendron Leaf blight, Dieback Leaf, Twig, Stem 

Vaccinium ovatum Huckleberry Canker, Dieback, Leaf blight Main stem, Branch, 

Leaf 

Fagaceae 

Castanea sativa Sweet chestnut Stem necrosis or canker; Leaf blight 

and necrosis Leaf, Stem 

Fagus sylvatica European beech Canker Trunk 

Lithocarpus densiflorus Tanoak Canker, Leaf blight Stem, Branch, Leaf 

Quercus agrifolia Coast live oak Canker Stem 

Quercus cerris European turkey oak Canker Trunk 

Quercus chrysolepis Canyon live oak Canker Sapling, Stem 

Quercus falcate Southern red oak Canker Bole 

Quercus ilex Holm oak Dieback Sprout 

Quercus kelloggii California black oak Canker Stem 

Quercus parvula var. 

shrevei Shreve oak Canker Stem 

Griseliniaceae 

Griselinia littoralis Griselinia Leaf necrosis Leaf 

Hamamelidaceae 

6 
 

 

Scientific Name Common Name Disease(s) Plant Part(s) 

Infected 

Hamamelis virginiana Witch hazel Leaf blight, Dieback Leaf, Twig 

Parrotia persica Persian ironwood Leaf necrosis 

Hippocastanaceae 

Aesculus californica California buckeye Leaf blight Leaf, Twig 

Aesculus hippocastanum Horse chestnut Canker Bole 

Lauraceae 

Laurus nobilis Bay laurel Leaf blight Leaf 

Umbellularia californica California bay laurel, Oregon 

myrtlewood, Pepperwood Leaf blight Leaf 

Liliaceae 

Maianthemum 

racemosum False Solomon’s seal Leaf blight Leaf 

Magnoliaceae 

Magnolia doltsopa Michelia Necrosis Leaf 

Oleaceae 

Fraxinus excelsior European ash Canker Trunk 

Syringa vulgaris Lilac Leaf Blight Leaf 

Pinaceae 

Pseudotsuga menziesii 

var. menziesii Douglas-fir Blight Branch, Needle (leaf) 

Primulaceae 

Trientalis latifolia Western starflower Blight Leaf 

Pteridaceae 

Adiantum aleuticum Western maidenhair fern Leaf necrosis Leaf 

Adiantum jordanii California maidenhair fern Leaf necrosis Leaf 

Rhamnaceae 

Frangula californica California coffeeberry Blight Leaf 

Frangula purshiana Cascara Blight Leaf 

Rosaceae 

Heteromeles arbutifolia Toyon Leaf blight, Dieback Branch, Leaf 

Photinia fraseri Red tip photinia Leaf blight Leaf 

Rosa gymnocarpa Wood rose Leaf blight Leaf 

Salicaceae 

Salix caprea Goat willow Leaf blight, Dieback Leaf, Twig 

Taxaceae 

Taxus baccata European yew Dieback Twigs at buds 

Taxodiaceae 

Sequoia sempervirens Coast redwood Needle blight Needle, Twig, Sprout 

Theaceae 

Camellia spp. Camellia Leaf blight; Less frequently, dieback Leaf, Petiole, Flower 

bud, Shoot, Twig 

Associated Plants (regulated only as Nursery Stock) 

Aceraceae 

Acer circinatum Vine maple Leaf necrosis Leaf 

Acer davidii Striped bark maple Leaf blight Leaf 

Acer laevigatum Evergreen maple Chlorotic leaves, Leaf necrosis Leaf 

Anacardiaceae 

Toxicodendron 

diversilobum Poison oak Canker Stem 

Apiaceae 

Osmorhiza berteroi Sweet cicely Leaf necrosis Leaf 

Aquifoliaceae 

Ilex purpurea Oriental holly Leaf blight, Leaf tip dieback Leaf 

Berberidaceae 

Berberis aquifolium Oregon grape Leaf blight Leaf 

Vancouveria planipetala Redwood ivy Leaf necrosis Leaf 

7 
Scientific Name Common Name Disease(s) Plant Part(s) 

Infected 

Betulaceae 

Corylus cornuta California hazelnut Leaf blight Leaf 

Calycanthaceae 

Calycanthus occidentalis Spicebush Leaf necrosis Leaf 

Celastraceae 

Euonymus 

kiautschovicus Spreading euonymus Shoot tip dieback, Leaf blight Shoot tip, Leaf 

Cornaceae 

Cornus kousa x Cornus 

capitata Cornus Norman Haddon Shoot tip dieback Shoot tip 

Dryopteridaceae 

Dryopteris arguta California wood fern Leaf blight Frond 

Ericaceae 

Arbutus unedo Strawberry tree Leaf blight Leaf 

Arctostaphylos 

Columbiana Manzanita Leaf necrosis Leaf 

Arctostaphylos uva-ursi Bearberry, Kinnikinnick Leaf necrosis Leaf 

Gaultheria shallon Salal, Oregon wintergreen Leaf blight Leaf 

Leucothoe axillaries Fetterbush, Dog hobble Leaf blight Leaf 

Leucothoe fontanesiana Drooping leucothoe Leaf blight Leaf 

Fagaceae 

Castanopsis 

orthacanthus Castanopsis Leaf chlorosis, Leaf necrosis (drip tip and mid-rib), Shoot tip die-back Leaf, Shoot 

Quercus acuta Japanese evergreen oak Canker Trunk 

Quercus petraea Sessile oak Canker Trunk 

Quercus rubra Northern red oak Canker Trunk 

Garryaceae 

Garrya elliptica Silk tassel tree, 

Coast silk tassel Leaf necrosis Leaf 

Hamamelidaceae 

Corylopsis spicata Spike witch hazel Leaf necrosis Leaf 

Distylium myricoides Myrtle-leafed distylium Leaf blight Leaf 

Hamamelis x intermedia, 

(H. mollis & H. 

japonica) 

Hybrid witch hazel Leaf blight Leaf 

Hamamelis mollis Chinese witch hazel 

Loropetalum chinense Loropetalum Leaf blight Leaf 

Lauraceae 

Cinnamomum camphora Camphor tree Shoot tip die-back, Stem necrosis or 

canker, Leaf chlorosis Shoot, Stem, Leaves 

Liliaceae 

Clintonia andrewsiana Andrew’s clintonia bead lily Leaf blight Leaf 

Magnoliaceae 

Manglietia insignis Red lotus tree Leaf blight, Tip dieback Leaf, Shoot 

Magnolia grandiflora Southern magnolia Leaf blight Leaf 

Magnolia stellata Star magnolia Leaf blight Leaf 

Magnolia x loebneri Loebner magnolia Leaf blight Leaf 

Magnolia maudiae Michelia Leaf blight Leaf 

Magnolia ernestii Michelia Leaf blight Leaf 

Magnolia x soulangeana Saucer magnolia Leaf chlorosis Leaf 

Parakmeria lotungensis Eastern joy lotus tree Leaf blight Leaf 

Myrsinaceae 

Ardisia japonica Ardisia Leaf blight Leaf 

Myrtaceae 

Eucalyptus haemastoma Scribbly gum Leaf chlorosis Leaf 

Nothofagaceae 

Nothofagus oblique Roble beech, Southern beech Canker Trunk 

8 
 

 

 

Scientific Name Common Name Disease(s) Plant Part(s) 

Infected 

Oleaceae 

Fraxinus latifolia Oregon ash Leaf blight Leaf 

Osmanthus decorus Osmanthus Leaf blight Leaf 

Osmanthus delavayi Delavay osmanthus, Delavay tea 

olive 

Shoot tip dieback, stem necrosis, or 

canker Shoot, Stem 

Osmanthus fragrans Sweet olive Leaf necrosis, Shoot tip dieback, Stem 

necrosis or canker Leaf, Shoot, Stem 

Osmanthus heterophyllus Holly olive Leaf necrosis Leaf 

Pinaceae 

Abies concolor White fir Leaf necrosis Leaf 

Abies grandis Grand fir Dieback, Leaf necrosis and bleeding 

canker Branch, Needle 

Abies magnifica Red fir Leaf blight, tip dieback Leaf, shoot 

Pittosporaceae 

Pittosporum undulatum Victorian box Leaf blight Leaf 

Rhamnaceae 

Ceanothus thysisflorus Blueblossom Leaf necrosis, stem necrosis or 

canker, canker Leaf, Stem, Trunk 

Rosaceae 

Physocarpus opulifolus Ninebark Leaf necrosis, dieback Leaf 

Prunus laurocerasus English laurel, Cherry laurel Leaf necrosis Leaf 

Prunus lusitanica Portuguese laurel cherry Leaf blight Leaf 

Pyracantha koidzumii Formosa firethorn Leaf blight Leaf 

Rosa (specific cultivars) 

Royal Bonica 

(“MEImodac”) 

 Pink Meidiland 

(“MEIpoque”) 

 Pink Sevillana 

(“MEIgeroka”) 

Hybrid roses Leaf blight Leaf 

Rosa rugosa Rugosa rose Leaf blight Leaf 

Rubus spectabilis Salmonberry Leaf blight Leaf 

Taxaceae 

Taxus brevifolia Pacific yew Dieback Needle, Twig 

Taxus x media Yew Stem base rot Stem 

Torreya californica California nutmeg Leaf necrosis, Shoot tip dieback Leaf, Shoot 

Theaceae 

Schima wallichii Chinese guger tree Shoot tip dieback Shoot 

Winteraceae 

Drimys winteri Winter’s bark Leaf blight, Dieback Leaf, Twig 1

Most current version is posted at: http//www.aphis.gov/plant_health/plant_pest_info/pram/ 

9 
 

 

 

 

C. Geographic Distribution 

Asia: No record 

Africa: No record 

Caribbean: No record 

Central America: No record 

Oceania: No record 

South America: No record 

Europe: Belgium, the Czech Republic (eradicated, Běhalová, 2006), Denmark, Finland 

(imported plants only), France, Germany, Ireland, Italy, Netherlands, Norway, Poland, Slovenia, 

Spain (Mallorca, Islas Baleares), Sweden, Switzerland, and the United Kingdom (Steeghs, 2007). 

North America: 

Mexico: No record. 

Canada: Infected ornamental plants in nurseries and landscape plantings have been detected and 

destroyed in British Columbia. 

United States: Fourteen counties in California (Alameda, Contra Costa, Humboldt, Lake, Marin, 

Mendocino, Monterey, Napa, San Francisco, San Mateo, Santa Clara, Santa Cruz, Solano, and 

Sonoma) and 116 square miles in Curry County, Oregon are currently under quarantine for 

P. ramorum (7 CFR §301.92; OSOS, 2007a, b). Infected nursery stock has been detected and 

destroyed in the following states: Alabama, Arkansas, Arizona, California, Colorado, 

Connecticut, Florida, Georgia, Louisiana, Maryland, Mississippi, North Carolina, New Jersey, 

New Mexico, New York, Oklahoma, Oregon, Pennsylvania, South Carolina, Tennessee, Texas, 

Virginia, and Washington (APHIS, 2005a). Since January 10, 2005, all nursery stock shipped 

interstate from California, Oregon, and Washington has been regulated to prevent movement of 

this pathogen (APHIS, 2004a, 2007b). 

Table 2. Plant genera with detections of Phytophthora ramorum in Europe. 

Country Detection Location Reference Nursery Outdoor Unknown 

Belgium Rhododendron, 

Viburnum 

RAPRA, 

2007 

Czech 

Republic Viburnum 

Běhalová, 

2006; 

RAPRA, 

2007 

Denmark Rhododendron Rhododendron, 

Viburnum 

RAPRA, 

2007 

Finland Rhododendron Rhododendron 

Lilja et al., 

2007; 

RAPRA, 

2007; 

Rythönen et 

al., 2007 

France Camellia, Pieris, 

RAPRA, 

2007 

Rhododendron, 

10 
 

 

 

 

 

 

Country Detection Location Reference Nursery Outdoor Unknown 

Viburnum 

Germany Rhododendron, 

Viburnum Pieris, Rhododendron Rhododendron, Viburnum 

Ireland Rhododendron Rhododendron, 

Viburnum 

Italy Rhododendron 

Netherlands Rhododendron, Taxus, 

Viburnum 

Fagus, Quercus, 

Rhododendron Viburnum 

Norway Rhododendron Rhododendron, Viburnum 

Poland Calluna, Photinia, 

Pieris, Rhododendron 

Slovenia Kalmia 

Spain 

Arbutus, Camellia, 

Rhododendron, 

Viburnum 

Aesculus, Arbutus, 

Camellia, 

Rhododendron, 

Syringa, Taxus, 

Viburnum 

Sweden Rhododendron Rhododendron 

Switzerland Rhododendron, 

Viburnum Viburnum 

United 

Kingdom 

Camellia, Garrya, 

Grisellinia, Hamamelis, 

Kalmia, Laurus, 

Leucothoe, Magnolia, 

Osmanthus, Parrotia, 

Pieris, Rhododendron, 

Syringa, Taxus, 

Viburnum 

Acer, Aesculus, Castanea, 

Castanopsis, Cinnamomum, 

Cornus, Cydonia, Drimys, 

Eucalyptus, Fagus, Fraxinus, 

Grisellinia, Hamamelis, 

Kalmia, Laurus, Magnolia, 

Michelia, Notofagus, Pieris, 

Quercus, Rhododendron, 

Schima, Syringa, Umbellularia, 

Viburnum 

Arbutus, Camellia, 

Hamamelis, Kalmia, 

Leucothoe, Lonicera, 

Magnolia, Pieris, 

Quercus, 

Rhododendron, Salix, 

Syringa, Taxus, 

Viburnum 

D. Biology and Epidemiology 

The disease cycle associated with P.ramorum (Fig. 1) is complex because of the variety of 

habitats where the pathogen occurs, the diversity of plants attacked, and the variation in plant 

response to infection (Davidson et al., 2003c). Phytophthora ramorum incites multiple diseases, 

with host dependent symptomology: bleeding canker (sudden oak death), e.g., on several 

members of Fagaceae; ramorum leaf blight, e.g., on U. californica; and ramorum dieback, e.g., 

on Q. ilex. Wilt symptoms have been observed on shoot tips of various hosts of 

P. ramorum and Parke et al. (2007) recently demonstrated a possible mechanism for a vascular 

wilt disease in L. densiflorus. 

Phytophthora ramorum produces sporangia, zoospores, and chlamydospores in culture and in 

nature (Davidson et al., 2003c; Parke et al., 2002a; Werres et al., 2001), and oospores under 

laboratory conditions (Boutet and Chandelier, 2007; Werres and Zielke, 2003). Sporangia are 

semi-papillate, caducous, and range in length from 20-80 μm (Rizzo et al., 2002b; Werres et al., 

2001). Chlamydospores are produced on hyphal tips and are hyaline, becoming brown with age 

and when produced on host tissue (Rizzo et al., 2002b; Werres et al., 2001). Chlamydospores 

range in size from 40-80 μm (Rizzo et al., 2002b) and 20-91 μm (Werres et al., 2001). Hyphae 

11 
 

 

of this species are nodose, highly branched, contorted, and form a dendritic pattern. 

Phytophthora ramorum is a poor saprophytic competitor (Rizzo et al., 2002b). 

Phytophthora ramorum is a heterothallic organism with two mating types, A1 and A2 (Werres et 

al., 2001). Originally, A1 isolates were found only in Europe (Werres et al., 2001) and A2 

isolates only in the United States (Rizzo et al., 2002b). The two mating types coincided with 

genetic differences and were determined to be distinct populations (Brasier, 2003; Brasier et al., 

2003; 2006a, b; Kroon et al., 2004). In 2003, an A2 isolate that matched the European 

population was detected on imported European nursery stock in Belgium (Werres and De 

Merlier, 2003). Also in 2003, A1 isolates were detected on nursery stock in Oregon, 

Washington, and British Columbia that matched the European A1 population (Hansen et al., 

2003a). 

Ivors et al. (2006) identified three lineages of P. ramorum, one from Europe and two from North 

America. These three lineages are based on microsatellite profiles and designated EU1, NA1, 

and NA2; the names correspond to the continent where the lineage was originally found (Table 

3; COMTF, 2007). The EU1 lineage, originally found in Europe, consists predominantly of A1 

isolates but also contains three A2 isolates from Belgium nurseries (RAPRA, 2007). The NA1 

lineage consists of A2 isolates that were detected in forests in California and Oregon or in 

nurseries in the United States and Canada. The NA2 lineage is rare and consists of A2 isolates. 

These NA2 isolates were found in or traced to nurseries in Washington and California. These 

different lineages have limited molecular variation, suggesting that they were introduced 

separately from a more variable original population (Ivors et al., 2006). 

Table 3. Summary of characteristics of the three lineages of Phytophthora ramorum. 

Lineage Mating Type Location 

NA1 A2 Forests in California and Oregon; Nurseries in U.S. and Canada 

NA2 A2 Nurseries in North America 

EU1 A1 Nurseries and wildlands in Europe; Nurseries in U.S. and Canada 

EU1 A2 Nurseries in Belgium 

Oospores have not been detected in nature, but have been observed in culture when P. ramorum 

strains are paired with other Phytophthora species representing opposite mating types (Boutet 

and Chandelier, 2007; Brasier and Kirk, 2004; Brasier et al., 2006a, b; Rizzo et al., 2002b; 

Werres et al., 2001). Boutet and Chandelier (2007) reported that gelling qualities of culture 

media and genotype influenced the formation of gametangia. A European A1 strain producing 

very few chlamydospores was found to be a better mating partner than other A1 strains. This 

research suggests that these oospores are the result of selfing and not hybridization between 

mating partners (Boutet and Chandelier, 2007). Oospores were reported on hyphae produced 

from a pairing of U.S. isolate PR6-2 with EU isolate BBA 9/95 on green Rhododendron twigs 

(Zielke and Werres, 2002). 

In culture, P. ramorum had optimum growth at 20°C (Werres et al., 2001), reduced growth at 

-1°C, and did not survive at -25°C (DEFRA, 2004c). However, one North American A2 isolate 

was found to grow optimally at 25°C (DEFRA, 2004c). 

12 
 

 

There are a number of studies on infection by P. ramorum (detached leaves, stems, roots, plants, 

and log segments). For example, detached leaf assays of Rhododendron found a positive 

correlation between lesion development and number of degree-days; the maximum temperature 

tested, 25°C, resulted in the largest lesions (DEFRA, 2004c). Garbelotto et al. (2003) found that 

9-12 hours of leaf wetness at 18-22°C are necessary to obtain significant infections on 

U. californica leaves. Brasier et al. (2007) demonstrated infection by zoospores through intact 

bark on log segments of F. sylvatica, Q. robur, and A. pseudoplatanus. Parke and Lewis (2007) 

observed P. ramorum penetrating Rhododendron roots at primordia, emerging laterals, and 

wound sites. They also noted that P. ramorum did not need stomata to infect leaves and that 

infections near the midrib resulted in more rapid disease development than infections at other 

leaf sites. 

Hosts of P. ramorum usually fall into one of two disease categories based on the plant part 

infected: “canker hosts” or “leaf and twig hosts” (Davidson et al., 2003b). The pathogen is 

polycyclic (Fig. 1) on most leaf and twig hosts (Davidson et al., 2003a, b, 2005). Infections in 

leaf and twig hosts are rarely fatal, but they can serve as a reservoir of the pathogen and a source 

of inoculum (DEFRA, 2004c; Parke et al., 2002b, c; Rizzo et al., 2002b). Sporangia and 

chlamydospores are produced abundantly on several foliar and dieback hosts, including 

U. californica (Davidson et al., 2002b), Rhododendron, and K. latifolia (DEFRA, 2004c). 

Differences in sporulation ability and susceptibility to infection have been reported for foliar and 

dieback hosts (DEFRA, 2004c; Dodd et al., 2002; Hansen et al., 2005; Hüberli et al., 2002; 

Linderman and Davis, 2007a; Parke et al., 2002a, b, c, 2006a; Tooley and Kyde, 2007; Tooley et 

al., 2004). 

In field tests, chlamydospores within host material were shown to overwinter down to -9°C in 

the United Kingdom (DEFRA, 2004c) and to oversummer in California (Fichtner et al., 2004, 

2006b, 2007a). Chlamydospore survival increased with depth of burial in both studies (DEFRA, 

2004c; Fichtner et al., 2006b). 

Canker hosts exhibit infections on basal stems (trunks of trees, stems of Viburnum) and often die. 

Sporulation was not observed on canker surfaces of these hosts (Davidson et al., 2003b, c), 

although exudates have tested positive with PCR (Tjosvold et al., 2002a). However, if the inner 

bark (cambium) is exposed and free water is present, the pathogen can sporulate on exposed 

surfaces (Davidson et al., 2003b, c). The pathogen has been recovered from inner bark 

(Davidson et al., 2003b), wood chips (Davidson et al., 2003b; Shelly et al., 2005b), and firewood 

stored for six months (Shelly et al., 2005a). Sporulation was stimulated in baiting trials when 

inoculated “logs” were kept at 12°C prior to baiting (Garbelotto, 2002). More recent studies 

have demonstrated that P. ramorum can occupy the xylem beneath phloem lesions, perennate in 

xylem tissue, and spread in xylem tissue ahead of phloem lesions (Brown and Brasier, 2007; 

Parke et al., 2007). 

The disease incidence of sudden oak death in California and Oregon is clustered. Spatial 

analysis in California indicated that diseased plants were clustered within 100 and 300 m of each 

other (Meentemeyer and Kelly, 2002). Disease incidence was correlated with proximity to forest 

edge, potential topographic moisture, abundance of U. californica, and potential solar radiation. 

However, Condeso and Meentemeyer (2007) found that elevation, temperature, and amount of 

13 
 

contiguous forest were correlated with disease incidence. In addition, the temperature range 

correlated with the highest disease incidence, 0-10°C, was lower than the optimal range observed 

for zoospore production (15-20°C) under laboratory conditions by Davidson et al. (2005). 

Long-distance dispersal includes movement of infected plant material (wood, green material 

products, and nursery stock), soil, water (rain, runoff, streams, rivers, irrigation water) (Davidson 

et al., 2002b, c), animals, and aerial dissemination (of sporangia, zoospores and possibly 

chlamydospores) during major weather events. It is postulated that long-distance dispersal 

through aerial dissemination is responsible for spread of the NA1-A2 mating type in California 

and Oregon (Hansen et al., 2002). 

E. Detection and Identification 

Symptoms 

Different diseases are attributed to P. ramorum: sudden oak death, stem or bole cankers, 

ramorum dieback, twig blight, and ramorum leaf blight (Table 1). Wilt symptoms have been 

observed on shoot tips of various hosts of P. ramorum (Parke et al., 2007; Storer et al., 2002). 

Symptomology has been addressed by Davidson et al. (2003b); Garbelotto et al. (2002a, 2003); 

Goheen et al. (2006b); Parke et al. (2003, 2004b); Storer et al. (2002); and Tjosvold et al. 

(2004). 

Prominent hosts in the nursery trade include Rhododendron, Camellia, Pieris, and Viburnum. 

Symptoms on Rhododendron mirror those incited by other species of Phytophthora and by 

certain environmental factors. This makes inspection for the disease more complicated 

(Davidson and Shaw, 2003) and detection more challenging (Jones et al., 2003). 

With Lithocarpus species, drooping or wilting of new growth may occur before other symptoms 

appear (Storer et al., 2002). Parke et al. (2007) recently demonstrated a possible mechanism for a 

vascular wilt disease in L. densiflorus. Cankers typically occur in the lower 3 meters and are 

restricted to above the soil line. Occasionally cankers have been found 20 meters above ground. 

Earlier research suggested that cankers girdled the tree, resulting in death. Current research 

indicates that infection by P. ramorum caused vessel blockage, resulting in wilt, and potentially, 

in tree mortality (Parke et al., 2007). Bleeding (oozing) symptoms of the canker are easier to 

detect during dry weather and become more difficult to detect during the rainy season, when the 

ooze is washed off. 

New Phytophthora species were described as a result of field analyses and surveys for 

P. ramorum: P. nemorosa E. M. Hansen and Reeser and P. kernoviae Brasier, Beales & S. A. 

Kirk (2005). Species new to the United States have also been found: P. hedraiandra and 

P. pseudosyringae. Phytophthora nemorosa and P. pseudosyringae occupy a similar ecological 

niche to P. ramorum in the United States (Hansen et al., 2003b) and P. kernoviae a similar niche 

in the United Kingdom (Brown and Brasier, 2007; DEFRA, 2004c, 2005a). Phytophthora 

hedraiandra was found on Viburnum tinus during nursery surveys in Minnesota (Schwingle et 

al., 2007), from Viburnum in the Netherlands (de Cock and Lévesque, 2004), and from V. tinus 

in Spain (Moralejo et al., 2006). These closely related species occupy the same niches and cause 

similar symptoms, thus confusing P. ramorum detection. 

14 
 

Isolation, Detection and Characterization 

Phytophthora ramorum can be isolated directly or indirectly (baiting with pear fruit or host 

leaves) from infected host material, soil, and water (Davidson et al., 2002a, 2003b; Goheen et 

al., 2002c; Maloney et al., 2002a; Rizzo et al., 2002a, b; Werres et al., 2001). Recovery rates 

vary with season and host (Davidson and Shaw, 2003; Hayden et al., 2004), and are facilitated 

with the use of the selective medium PARP (Davidson et al., 2003b). Additionally, preliminary 

results indicate that exposure of infected woody material to a cool temperature, 12°C 

(Garbelotto, 2002), and plating the samples on PARP immediately following collection in the 

field (Storer et al., 2002) will facilitate recovery of the pathogen. Samples are incubated in the 

dark at 20o

 to 22oC and examined within seven days. 

Morphological and molecular comparisons of U.S. and European isolates indicate that the two 

mating types are the same species (Ivors et al., 2004; Man in’t Veld et al., 2002; Zielke and 

Werres, 2002). Pogoda and Werres (2002) found that growth rate and colony morphology were 

related to aggressiveness. Slow vegetative growth, exhibited by many U.S. isolates, was 

correlated with mild twig infection. Although the European isolates have greater genetic 

diversity than the U.S. isolates, they are more phenotypically similar. 

Polymerase chain reaction (PCR) methods are used for the detection and identification of this 

pathogen (Hayden et al., 2004; Martin and Tooley, 2001; Martin et al., 2002, 2004). Hayden et 

al. (2004) found PCR and isolation frequency varied with season and host, but PCR detection 

was more sensitive than isolation. Maloney et al. (2004) first detected P. ramorum in madrone 

by PCR and later were able to isolate the pathogen. Arctostaphylos manzanita was found to be 

positive by PCR (Rizzo et al., 2002a) long before isolation attempts were successful. 

Molecular analysis found that 83 isolates (65 U.S., 18 European) were identical at three DNA 

regions (ITS, cox II, and nad 5) (Ivors et al., 2004). Amplified Fragment Length Polymorphism 

(AFLP) analysis indicated that a single clonal lineage dominated the U.S. isolates. Two U.S. 

isolates from an Oregon nursery differed at those regions. Microsatellite analysis of over 200 

isolates revealed seven loci that discriminated between U.S. and European isolates (Prospero et 

al., 2005, 2007). Microsatellite analysis of 151 isolates of P. ramorum revealed three distinct 

clades: the U.S. population, the European population, and one unique population (Ivors et al., 

2006). 

Two molecular detection methods have been validated by USDA APHIS (CPHST, Beltsville, 

MD) for use in regulatory determinations of P. ramorum. The APHIS nested PCR protocol is 

based on Hayden et al. (2004), with a multiplex PCR quality control component from Winton 

and Hansen (2001). APHIS also uses a real-time PCR protocol based on Hughes et al. (2006). 

Nested PCR occasionally has cross-reactions with P. lateralis (Blomquist and Kubisiak, 2003) 

and P. foliorum (Donahoo et al., 2006). Safeguards are included in the USDA protocol to 

identify and prevent misdiagnosis. New procedures are being evaluated for inclusion for use in 

the regulatory program, including work by Schena et al. (2006), Martin et al. (2004) and 

Bilodeau et al. (2007). 

ELISA can be used to detect species of Phytophthora (Brown and Brasier, 2007; Bulluck et al., 

2007). This method may be used to facilitate the processing of large number of samples and is a 

part of the USDA protocol (APHIS, 2006). All ELISA positive samples must be tested by 

15 
approved PCR methods to confirm the presence of P. ramorum. Approved PCR methods can be 

run by the Molecular Diagnostic Laboratory, which is part of the National Identification 

Services, or by the laboratories approved by the National Plant Protection Laboratory Approval 

Program. 

Monitoring 

The National Phytophthora ramorum Survey, a nursery inspection program, ended in 2006; 

however, nursery surveys continue under a Federal Order (effective January 10, 2005) restricting 

movement of infected plants from California, Oregon, and Washington. This order also required 

that both host and non-host nurseries be inspected to move nursery stock interstate and that traceforward and trace-back activities be conducted once positive nursery material is detected. 

16 
Legend 

? 

? 

? 

? 

? 

? 

? 

? 

Dormancy or resting state 

broken in Chlamydospores 

Dormancy or other 

resting state induced in 

Chlamydospores or 

Mycelia 

Dormancy or resting 

state broken in Mycelia 

Chlamydospores 

Sporangia 

Susceptible Plant 

Tissue: Roots/Fallen 

Green Leaves 

Direct germ

Spores washed/blown to 

ground 

Infected tissue falls to 

ground or on surface of 

potting medium 

Inoculum in soil/growing 

medium Sporulation in or on leaves and 

twigs 

Host material harvested for 

wood products: inner bark 

exposed 

Outer bark breeched and 

inner bark infected 

Inoculum splashed onto 

susceptible host 

Sporulation at water surface 

from exposed inner bark 

Host Infected 

Foliar and 

dieback 

Canker host 

phase 

Soil/medium 

phase 

Dormancy 

phase 

Fig. 1. Possible disease cycle for sudden oak death, ramorum leaf blight, and ramorum dieback. Color is used to designate differ

17 
In addition, individual States may continue surveys through the USDA Cooperative Agricultural 

Pest Survey (CAPS) program. The USDA Forest Service continues to conduct a national survey 

program of forests and streams with a focus on areas adjacent to nurseries 

(http://fhm.fs.fed.us/sp/sod/sod.shtm). 

Aerial surveys of forests are conducted annually to survey for damaged L. densiflorus in Oregon 

(Anon., 2007; Goheen et al., 2002d) and for Quercus spp. and L. densiflorus in California (Bell 

and Fischer, 2006; Levien et al., 2002). Maps and additional data can be found at: 

http://www.oregon.gov/ODF/PRIVATE_FORESTS/fh.shtml (Oregon Reports) 

http://www.fs.fed.us/r6/nr/fid/data.shtml (Oregon data and maps) 

http://www.fs.fed.us/r5/spf/fhp/fhm/sod/index.shtml (California) 

http://kellylab.berkeley.edu/SODmonitoring/ (California) 

Airborne Digital Acquisition and Registration (ADAR) imagery based on red, green, blue, and 

near-infrared wavelengths was tested for capability to map species (Kelly and Meentemeyer, 

2002). Results were variable, but more promising for species mapping than for locating 

moisture-stressed trees. The USDA Forest Service currently uses an advanced digital sketching 

mapping system for aerial surveys (Anon., 2007). 

Aerial surveys are used, in conjunction with risk models, e.g., Meentemeyer et al (2004), to 

target areas for ground surveys (Bell and Fischer, 2006). Field visits resulted in ten new P. 

ramorum detections. The positive detection in southern Monterey County in the Willow Creek 

watershed is the farthest south the pathogen has been found to date. This watershed was targeted 

for field survey because a stream bait tested positive for P. ramorum in 2005. 

In 2006, a pilot survey was conducted to evaluate existing stream baiting and lab diagnostic 

methods for inclusion in the 2007 national P. ramorum early detection survey protocol. Streams 

in eleven States were surveyed, including ramorum-endemic (CA, OR), nursery-confirmed or 

nursery-introduced (GA, MD, NC, PA, TN, VA, WA), and states where P. ramorum has yet to 

be detected (KY, WV) (Oak et al., 2007). 

IV. Organism Risk Assessment 

A. Prior Risk Assessments, Current Status, and Interceptions 

On February 14, 2002, regulations were published to control the movement of P. ramorum from 

twelve infested counties in California and an area under eradication in Oregon. Various agencies 

within USDA (Agriculture Research Service, Forest Service, and Animal and Plant Health 

Inspection Service), universities and other institutions continue to conduct research and 

developmental studies to better identify hosts, methods of detection, and effective treatments. 

There are no chemical treatments currently available to eliminate the pathogen in nursery stock. 

In April 2004, a Federal Order was issued to address a concern of P. ramorum moving via 

nursery stock from California, Oregon, and Washington. On December 21, 2004, APHIS issued 

an emergency Federal Order that bolstered the Agency’s initial P. ramorum restrictions by 

regulating the interstate movement of plants for planting, including houseplants and propagative 

18 
materials, from all commercial nurseries in California, Oregon, and Washington. The Federal 

Order, which became effective on January 10, 2005, was enacted in response to detections of P. 

ramorum at commercial nurseries in California, Oregon, and Washington that are outside 

quarantined areas, and addresses a number of concerns regarding the adequacy of previous 

Federal P. ramorum restrictions. 

The USDA Forest Service conducted a risk assessment in 2001 with revisions in 2003, and 2005 

(Kliejunas, 2001, 2003, 2005). Other risk analyses have been produced by the Canadian Food 

Inspection Agency (Cree et al., 2001; Cree, 2002; Rioux et al., 2006), the UK Department of 

Environment, Forestry and Rural Affairs (Jones, 2002; Jones et al., 2003), the Oregon 

Department of Agriculture (ODA, 2001) and USDA APHIS (Cave et al., 2005). Currently, a 

PRA is under development by members of the European Union (RAPRA, 2007). 

Phytophthora spp. are difficult to detect by visual inspection, because disease symptoms are not 

always distinctive and the defining characteristics of the disease are not visible to the naked eye. 

There have been 12 interceptions at U.S. ports since January 1, 1985; of these, four were 

identified to species (none were P. ramorum). 

B. Consequences of Introduction 

This portion of the assessment considers negative outcomes that may occur when the hosts of 

P. ramorum provide a pathway of entry into the United States from infested countries as well as 

domestic movement of infested plant material. The potential consequences are evaluated using 

five Risk Elements (APHIS, 2002): Climate-Host Interaction, Host Range, Dispersal Potential, 

Economic Impact, and Environmental Impact. These risk elements reflect the biology, host 

range, and climatic and geographic distribution of this pathogen, and are supported by biological 

information. For each risk element, a rating of Low, Medium, or High 

is assigned (APHIS, 2002). Additionally, specific pathways, i.e., plants for planting, wood, soil, 

potting media, cut flowers/foliage, greenwaste, and compost, will be evaluated using these 

Elements. 

Risk Element 1: Climate-Host Interaction 

This risk element considers ecological zonation and the interactions of P. ramorum with its hosts 

in a variety of environments. When introduced into new areas, pests are expected to behave as 

they do in their native areas if the potential host plants and suitable climate are present. Broad 

availability of suitable climates and a wide distribution of suitable hosts are assumed to increase 

the impact of a pest introduction. The rating for this risk element is based on the number of 

United States Plant Hardiness Zones (USDA, 2003). 

Phytophthora ramorum has a high probability of encountering favorable climatic conditions 

throughout the ranges of potential hosts. Modeling of environmental conditions suggests that 

there are many areas in the United States which have both favorable conditions for disease 

development and susceptible hosts (Linderman et al., 2007; Magarey et al., 2004, 2007; Smith et 

al., 2002) (Fig. 2). Climate potential was higher on the West Coast and east of the Mississippi 

River than in the Central Plains. The risk to the more arid Central Plains states increases when 

humid microclimates, such as in plant nurseries or irrigated landscapes, are created. This 

19 
occurred during 2003 and 2004 in California when nurseries outside the quarantine zone and in a 

warmer and more arid environment shipped infected nursery stock (Magarey et al., 2004). 

The risk rating is High for the Climate-Host Interaction Risk Element. The level of 

certainty for this risk rating is fairly certain. Most of the eastern United States has 

actual and potential hosts growing in climates conducive to infection. The uncertainty 

lies in the range of biotic and abiotic factors triggering establishment of P. ramorum in 

new areas. 

Risk Element 2: Host Range 

The risk posed by a plant pest depends on both its ability to establish a viable, reproductive 

population and its potential to damage plants. This risk element assumes that the consequences 

of pest introduction are positively correlated with the pest’s host range. Aggressiveness, 

virulence, and pathogenicity also may be factors. The consequences related to host range are 

rated in accordance with the ability of the pathogen to attack a single species or multiple species 

within a single genus, a single plant family, or multiple families. 

The host range of this pathogen continues to expand through detections in the field. APHIS 

currently regulates over 109 plants in 35 families and 70 genera (Table 1). The potential host 

range is also increasing (APHIS, 2007b; DEFRA, 2006; Hansen et al., 2005). Experimental 

evidence demonstrates that several eastern forest species would be more susceptible than western 

forest species. In addition, differences in host susceptibility are documented for forest and 

nursery species and may impact disease development in new environments (DEFRA, 2004c; 

Meshriy et al., 2005; Tooley et al., 2004). 

Brasier et al. (2002) screened several forest species by inoculating the inner bark of logs with 

U.S. and European P. ramorum isolates. This study suggested the most susceptible species in 

the United Kingdom are Q. rubra, Q. cerris, Q. ilex, F. sylvatica, C. sativa, P. sitchensis, P. 

menziesii var. menziesii, and C. lawsonia. Since this study, several of those species have been 

found naturally infected by P. ramorum during surveys in Europe: Q. rubra in the Netherlands, 

and Q. falcata, Q. ilex, Q. cerris, F. sylvatica, and A. hippocastanum in the United Kingdom 

(DEFRA, 2006). 

Tree species in the red oak/black oak group appear to be highly susceptible to P. ramorum. 

Greenhouse studies have compared susceptibility of regulated Quercus species to non-regulated 

Quercus species. Based on adjusted lesion area, two- to three-year old seedlings of Q. rubra, 

Q. montana (syn. Q. prinus), and Q. pagoda were found to be more susceptible to P. ramorum 

than the regulated host, Q. agrifolia (Tooley and Kyde, 2007). Quercus phellos, Q. nigra, 

Q. virginiana, and Juglans nigra were equally susceptible and A. saccharum was less susceptible 

than Q. agrifolia (Tooley and Kyde, 2007). In foliar inoculations, Q. montana (Q. prinus) was 

more susceptible that L. densiflorus; other Quercus species were significantly less susceptible 

(Tooley and Kyde 2007). 

Certain white oak species (Q. douglasii, Q. lobata, and Q. robur) are not as susceptible to 

P. ramorum as red oak species (Brasier et al., 2002; Rizzo et al., 2002a). Lesions on young 

white oak trees were similar in size to those on the wounded non-inoculated trees. However, 

20 
 

two- to three-year old seedlings of Q. alba were more susceptible to P. ramorum than those of 

the red oak species, Q. agrifolia (Tooley and Kyde, 2007). 

The large number of hosts in multiple plant families, differential susceptibility, and 

virulence warrant a risk rating for Host Range of High. The level of certainty for this risk 

rating is High. Phytophthora ramorum already has a large documented host range. The 

uncertainty for the rating for this element lies in not knowing the extent of the host range. 

Risk Element 3: Dispersal Potential 

Pests may disperse after introduction into new areas. The dispersal potential indicates how 

rapidly and widely the pests may spread. This factor is related to the pest’s reproductive 

potential, inherent mobility, and external dispersal facilitation modes within the importing 

country or region. Factors for rating the dispersal potential include: the presence of multiple 

generations per year or growing season, the relative number of offspring or propagules per 

generation, any inherent capabilities for rapid movement, the presence of natural barriers or 

enemies, and dissemination enhanced by wind, water, vectors, or human assistance. 

The scattered pattern of sites where P. ramorum has become established suggests that it has a 

mechanism of long-distance dispersal. Strong winds common during heavy rains along the 

California coast may move the easily detached sporangia great distances (Hansen et al., 2002). 

Initial survey results in California and Oregon indicate P. ramorum is in streams and rivers 

adjacent to and far from known infested areas (Murphy et al., 2006; Hansen et al., 2005). 

Inoculum has been detected seasonally from soil on hiking trails and from soil on hikers’ boots 

(Davidson et al., 2002c, 2005; Tjosvold et al., 2002b). The concerns about soil and litter 

movement by equipment have prompted California authorities to request that vehicles and other 

equipment, including tents and shoes, be washed prior to leaving a P. ramorum-infested area 

(COMTF, 2004a). 

In 2004, confirmed positive sites from the trace-forward, national, and other surveys totaled 176 

in 22 States (APHIS, 2005b, c). The total included three residential finds (Georgia, South 

Carolina), and one detection (PCR only) in the environs (New York) which prompted repeated 

testing. This area was finally released in 2007 (DA-2007-03, February 15, 2007). As of January 

10, 2005, all nursery stock shipped interstate from California, Oregon, and Washington is 

regulated to prevent movement of this pathogen (APHIS, 2007b). In 2004, 665 Christmas tree 

plantations in Oregon and 100 in Washington were surveyed and found negative for P. ramorum 

(COMTF, 2004b). 

Many of the hosts on the regulated host and associated plants lists are major nursery, forest, and 

understory species (Davidson et al., 2003b), and the host range is expanding. Evidence exists 

that several eastern forest species would be as susceptible as those affected in California and 

Oregon. Additionally, environmental conditions in areas in the eastern United States are 

predicted to be more conducive to disease development than in the majority of the western 

United States (Magarey et al., 2004, 2007). 

21 
 

Newly established populations may go undetected for years. The disease was first noted in 

California in 1995 (Garbelotto et al., 2001). With the rate of oak death, researchers suggest that 

the pathogen was introduced at least five years before the first detection (Rizzo and Garbelotto, 

2003). 

In the United States, both regulated and associated hosts are widely distributed, 

overlapping, abundant, and susceptible. In addition, the pathogen is polycyclic; 

infections may remain undetected for years. Long-distance dispersal has been 

documented via trade and natural means. For these reasons, the rating for P. ramorum 

is High for Dispersal Potential. The level of uncertainty for this rating is low based on 

the evidence of human-assisted and natural movement. 

Risk Element 4: Economic Impact 

Introduced pests cause a variety of direct and indirect economic impacts, such as reduced yield, 

reduced commodity value, loss of foreign or domestic markets, and non-crop impacts. Factors 

considered during the ranking process included the following: effect on yield or commodity 

quality; plant mortality; ability to act as a disease vector; increased costs of production, including 

pest control costs, lower market prices, effects on market availability, increased research or 

extension costs, or reduction in recreational land use or aesthetic value; ability of the pest to 

attack the hosts or products with significant commercial value, to directly cause tree mortality, or 

to predispose the host to mortality by other organisms; impact of the pest on the value of the 

affected host (e.g., by lowering its market price, increasing cost of production, maintenance, or 

mitigation, or reducing value of property where it is located); and lack of effective control 

measures. 

The USDA had spent more than $55 million by the end of 2005 on regulatory, research, and 

educational issues related to P. ramorum (Table 4). This value does include state and local 

government and industry expenditures. 

California’s oak woodlands contain about 5 billion cubic feet of wood valued at over $275 

million (Kliejunas, 2003). The nearby California timberlands contain 5.8 billion cubic feet of 

oaks, which are worth over $500 million for forest products alone (Kliejunas, 2003). Oak 

products exported from California from 1996-2000 averaged almost $50 million per year 

(USITC, 2005). 

Phytophthora ramorum presents a potential economic threat to eastern U.S. oaks. Two oak 

species native to the eastern United States, Q. rubra and Q. falcata, were found naturally 

infected in Europe (Brasier et al., 2004b; EPPO, 2004). Susceptibility of other eastern U.S. tree 

species (Q. alba, Q. laurifolia, Q. nigra, Q. pagoda, Q. phellos, Q. montana (syn. Q. prinus), 

Q. virginiana, A. saccharum, and J. nigra) has been experimentally demonstrated (Brasier et al., 

2002; Linderman et al., 2007; Tooley and Kyde, 2007) and represents a potential economic 

threat to commercial timber production in the United States exceeding $30 billion (Kliejunas, 

2003). The export value of red oak logs and lumber was over $300 million dollars in 2002 

(USITC, 2005). 

22 
In coastal central California, oak woodland suitable for residential development has been 

estimated at $20,000 per acre; rangeland with at least 40 oaks per acre was worth 27 percent 

more than open land (Standiford, 2000). In southwestern Oregon, mature black oak trees can 

increase property values by $5,000-30,000 (Osterbauer, 2003). 

Current regulations require debarking of the logs in order to send them to pulp mills outside 

quarantine areas (COMTF, 2003). Hardwood hosts are used for firewood, wood chips for 

pulping, compost, non-grade lumber, and charcoal. Higher value uses include custom furniture, 

flooring, cooperage, and tool handles (Shelly et al., 1996). 

The U.S. nursery industry is also at risk. Nursery crops include woody perennial plants, such as 

ornamental trees, shrubs, and vines, which are primarily used for landscaping. In 2006, the U.S. 

domestic production of nursery crops was valued about $12.9 billion. Imports for these crops 

were $341 million and exports were $287 million (Jerado, 2007). 

Tourism is also affected, as visitors to parks and forests may find that access to selected areas is 

restricted during certain seasons to prevent movement of the pathogen or to protect visitors from 

falling limbs from trees killed by P. ramorum. When visitors are requested or required to take 

precautions to prevent its movement, park and forest staff may be required to provide 

educational information, staff cleaning areas, and provide appropriate supplies and equipment to 

remove soil from shoes and vehicles (COMTF, 2004a). 

The presence of P. ramorum has resulted in restrictions in foreign and domestic trade. Australia, 

Canada, Korea, New Zealand, the European Union, and Switzerland have placed restrictions on 

the movement of affected plants and plant parts from the United States (EXCERPT, 2007; Rizzo 

and Garbelotto, 2003). In addition, the United States has placed restrictions on the movement of 

propagative material from the European Union (Aley, 2007). 

The evidence to date is that P. ramorum impacts the domestic movement of plants and 

plant products (nursery stock, fruit, logs, lumber, etc.) and has restricted international 

trade. For these reasons, the economic impact of P. ramorum is rated High. Uncertainty 

depends on the relationships between the extent of the host range and the value of these 

plants on the open market. 

23 
Fig. 2. Overall risk index for the establishment of Phytophthora ramorum in the continental United States based on introductio

number of plants shipped from an infested nursery), climate potential (leaf wetness, temperatures, and relative humidity based 

economic potential, and host strength (quantity and diversity of potential hosts) (Magarey et al., 2004). 

24 
Table 4. Summary of USDA funding for Phytophthora ramorum, Fiscal Years 2000-2005. 

Funding, by USDA agency (Dollars in Millions) 

Fiscal year Forest 

Service 

Animal and 

Plant Health 

Inspection 

Service 

Agricultural 

Research 

Service 

Cooperative State 

Research, 

Education and 

Extension Service 

Total 

2000 $0.12 $0.00 $0.00 $0.00 $0.12 

2001 4.20 0.00 0.00 0.00 4.20 

2002 0.97 0.90 0.00 0.00 1.87 

2003 3.70 2.00 0.62 0.30 6.62 

2004 3.70 19.50 1.30 0.30 24.80 

2005 4.40 12.40 1.00 0.12 17.92 

Total $17.09 $34.8 $2.92 $0.72 $55.53 

Source: United States Government Accountability Office Report to the Chairman, Committee on Resources, House of 

Representatives report on Invasive Forest Pests, April, 2006, Page 109 (http://www.gao.gov/new.items/d06353.pdf) 

Risk Element 5: Environmental Impact 

The ratings for this risk element are based on three aspects: the potential of the pest to disrupt 

native ecosystems and habitats exhibited within its current geographic range, the need for 

additional chemical or biological control programs due to the presence of the pest, and the 

potential of the pest to directly or indirectly impact species listed as Threatened or Endangered 

(50 CFR §17.11-12) by infesting or infecting a listed plant. When a pest is known to infest or 

infect other species within the same genus, and host specificity data does not exist for the listed 

plant, then the listed plant is assumed to be a potential host. 

In forests, more than 20 non-indigenous species of plant pathogens attack woody plants 

(Liebhold et al., 1995). Two of the most destructive plant pathogens are Cryphonectria 

parasitica and Ophiostoma ulmi, the causal agents of chestnut blight and Dutch elm disease, 

respectively. Before the introduction of chestnut blight, approximately 25% of eastern U.S. 

deciduous forest consisted of American chestnut trees (Castanea dentata) (Liebhold et al., 1995). 

These trees have all but disappeared. In urban and forest environments, species and cultivars of 

Ulmus have been destroyed by O. ulmi. The environmental costs of prevention, eradication, or 

suppression of this pathogen include indirect ecological consequences (perturbations of 

hydrological cycles, e.g., flood control and water supply, waste assimilation, nutrient recycling, 

conservation and regeneration of soils, crop pollination) and must address both current-use value 

and future-use values. 

Quercus species are the most important and widespread of the hardwood trees in the North 

Temperate Zone (Pavlik et al., 1991, as cited in Kliejunas, 2003). These woodlands yield 

important benefits, such as water and watershed protection, grazing, wildlife food and habitat, 

recreation, and wood products (Monahan and Koenig, 2006; Thomas, 1997); are known for their 

scenic beauty; and contribute to tourism and high property values. The loss of keystone Quercus 

species in these forests would be detrimental to forest health. In addition, the effects on rare and 

endangered plant species in these regions are unknown. Phytophthora ramorum is expected to 

cause significant direct environmental effects, such as extensive ecological disruption or large25 
scale reduction of biodiversity. This pathogen has already caused environmental damage with 

the death of thousands of Quercus and Lithocarpus trees. The loss of one particular oak species, 

Q. agrifolia, has been shown to negatively impact the populations of five California bird species 

(Monahan and Koenig, 2006). Barrett et al. (2006) have indicated that dozens of wildlife species 

would be negatively affected by the loss of L. densiflorus, Q. kelloggii, and Q. agrifolia and the 

associated loss of food, nesting, and den sites. 

A number of genera on the APHIS Host and Associated Plants Lists have species on the U.S. 

Fish and Wildlife Service Threatened and Endangered Species List (USFWS, 2007). These are 

Arctostaphylos confertiflora, A. glandulosa ssp. crassifolia, A. hookeri var. ravenii, A. 

morroensis, A. myrtifolia, A. pallida, Prunus geniculata, Q. hinckleyi, and R. chapmanii. 

The rating for Environmental Impact is High. The uncertainty lies with the difficulty in 

producing estimates for the costs of P. ramorum that address all of the relevant ecological 

components. These include: (1) the environmental costs of prevention, eradication, or 

suppression due to herbicide use; (2) the effects on endangered species; and (3) the indirect 

ecological consequences (changes in locally important ecological processes such as 

perturbations of hydrological cycles, e.g., flood control and water supply, waste 

assimilation, nutrient recycling, conservation and regeneration of soils, and crop 

pollination and habitat destruction). 

C. Likelihood of Introduction 

The Likelihood of Introduction for a pest is rated relative to three factors and is based on APHIS 

PRA guidelines (APHIS, 2002). The first factor, Entry Potential, is based on the volume of 

materials moved domestically and internationally, the value of these shipments, and the 

likelihood that the pathogen will survive post-harvest treatments and shipment. The second 

factor, Establishment and Spread Potential, includes the likelihood that the pathogen will be 

imported or moved to an area suitable for survival and will encounter host material. The third 

factor, Detection Potential, is an estimation of the likelihood that the pathogen will not be 

detected at ports-of-entry or during domestic inspections. 

Subelement 1: Entry Potential 

The rating for this risk element is based on the volume and value of domestic shipments and 

imports from Europe and Canada and on the ability of the pathogen to survive post-harvest 

treatments and shipment. The volume of plants for planting from Europe increased from 

approximately 33 million plants in 2000 to 47 million plants in 2003, and dropped to 38 million 

plants in 2004 (Table 5); the drop was possibly a result of restrictions on the imports of regulated 

hosts of P. ramorum. 

Live plants are grown, shipped, and sent to areas conducive to their survival. Plant products, 

such as cut flowers and foliage will also be treated in ways not detrimental to the survival of 

P. ramorum. For example, P. ramorum has been detected in nursery stock shipped from 

California to 21 other states and eradicated in nurseries in which it was detected. In addition, 

models (Kluza et al, 2007; Magarey et al., 2004, 2007; Smith et al., 2002) have indicated that 

most of the eastern United States has both potential hosts and favorable conditions (Fig. 3). 

26 
Living plants are not likely to receive post-harvest treatments such as irradiation, methyl 

bromide, or steam sterilization because these treatments would likely kill the plants as well as the 

pests. In addition, the presence of potting media requires specific testing to ensure the efficacy 

of any proposed post-harvest treatments (Jarvis, 1992). General transport conditions for potted 

plants range from 10-18°C and 85- 90% relative humidity (McGregor, 1987). Phytophthora 

ramorum has an optimum temperature range of 18-25°C (DEFRA, 2004c; Werres et al., 2001) 

and survives temperatures as low as -9°C (DEFRA, 2004c). 

Although not handled as gently as live plants and cut flowers/foliage, other infested plant 

products such as logs, lumber, wood chips, and firewood may harbor the pathogen and present a 

pathway for introduction into new areas. For example, P. ramorum has been recovered from 

inner bark and wood chips (Davidson et al., 2003b), suggesting that when the inner bark is 

exposed, as in the debarking process, and free water is present, the pathogen can sporulate on the 

exposed surfaces. Additionally, sporulation was stimulated in baiting trials when inoculated 

“logs” were kept at 12°C prior to baiting (Garbelotto, 2002) and the pathogen has been recovered 

from firewood stored for six months (Shelly et al., 2005a). For these reasons, the rating for this 

Subelement is High. 

Subelement 2: Establishment and Spread Potential 

Suitable hosts must be available to establish and sustain a pest population, and there must be a 

mechanism for the pest to reach these hosts. Both natural and human-assisted factors aid in the 

dispersal of P. ramorum (Davidson et al., 2003a; Davidson and Shaw, 2003; Hansen et al., 

2002). This pathogen infects 70 genera in 35 plant families (Table 1). Many of these hosts are 

widely distributed in the United States, and conducive climatic conditions are prevalent along the 

East and West Coasts (Fig. 3). In woody canker hosts, sporulation is not observed on the surface 

of cankers (Davidson and Shaw, 2003). However, if the inner bark (cambium) is exposed and 

free water is present, the pathogen can sporulate on exposed surfaces, e.g., the pathogen has 

been recovered from inner bark, wood chips (Davidson and Shaw, 2003) and from firewood 

stored for six months (Shelly et al., 2005a). Sporulation in baiting trials was stimulated when 

inoculated “logs” were kept at 12°C prior to baiting (Garbelotto, 2002). In several tree species, 

the xylem has recently been shown to harbor mycelia and chlamydospores of P. ramorum 

(Brown and Brasier, 2007; Parke et al., 2007). For these reasons, the rating for this Subelement 

is High. 

Subelement 3: Detection Potential 

Species of Phytophthora, such as P. ramorum, are difficult to detect at ports-of-entry, where 

visual inspection is the primary method of detection; Phytophthora spp. have only been detected 

12 times since 1985 (PPQ, 2007a). In addition, there are recent reports of asymptomatic 

infection and sporulation (Denman et al., 2008; Vettraino et al., 2007). Other pathogens and 

environmental conditions can elicit the same symptomology in foliar and dieback hosts. Two 

newly detected Phytophthora species, P. nemorosa and P. kernoviae, induce similar cankers on 

trees and were found as a result of field analyses for P. ramorum. P. nemorosa occupies a 

similar ecological niche to P. ramorum in the United States (Hansen et al., 2004) and 

P. kernoviae a similar niche in the United Kingdom (Brasier et al., 2004a, 2005; DEFRA, 

2004a). 

27 
 

Isolation techniques, including direct plating and baiting, are used to detect the pathogen in plant 

tissues, soil, and water. The efficacy of these techniques varies with season and host (Davidson 

et al., 2002c). Molecular detection techniques include ELISA (at the genus level), AFLP, and a 

variety of PCR protocols. Nested and real-time PCR methods are currently used for regulatory 

purposes in the United States (PPQ, 2007b) and real-time PCR methods are used in the United 

Kingdom (Lane et al., 2007). The internal transcribed spacer (ITS) DNA analysis does not 

always distinguish P. ramorum from P. lateralis (Blomquist and Kubisiak, 2003) and 

P. foliorum (Donahoo et al., 2006); however, multiplex methods can increase sensitivity. The 

possibility of failure of visual inspection to detect latent infections is a concern. 

The disease was first noted in California in 1995 (Garbelotto et al., 2001) and, based on the rate 

of oak death, researchers suggest the pathogen was introduced at least five years before the first 

detection (Rizzo and Garbelotto, 2003). Since that time, survey and diagnostic methods have 

improved, thereby increasing the likelihood of detecting the pathogen. Nevertheless, for the 

above reasons, the rating for this Subelement is High. 

The rating for Likelihood of Introduction is High. Both natural and human-assisted 

factors aid in the dispersal of P. ramorum to areas where suitable hosts and climatic 

conditions are available and conducive to establishing and sustaining a population. 

Differences in sporulation ability and susceptibility to infection have been reported for 

foliar, dieback, and canker hosts. The uncertainty lies with the variability in detecting P. 

ramorum and the ability to predict the levels of resistance and susceptibility among hosts 

and potential hosts occurring in non-infested regions. 

D. Pest Risk Potential 

The Consequences of Introduction and the Likelihood of Introduction are rated High; therefore, 

the Pest Risk Potential is High. The overall risk presented by P. ramorum is High due to the 

number of pathways associated with and the biological uncertainties of the pathogen, e.g., the 

demonstrated long-distance dispersal in trade, long-term viability of infective propagules, 

detection of the propagules, lack of definitive host range, the sensitivity of detection of infected 

plants by visual inspection, and means of natural movement. Research is needed on dormancy in 

chlamydospores; increased sensitivity and specificity of detection techniques; temperature 

requirements for survival of propagules in various sources, e.g., soil, wood; risk of moving the 

pathogen in various species and hybrids; screening for more potential hosts including products 

and propagative material of vegetable, fruit, and nut crops; and natural dispersal, especially 

animal and aerial dispersal. The lack of a definite host range and a definitive geographic 

distribution adds to the pest risk potential. 

28 
Table 5. Imports of plant materials from Europe and Canada to the United States (quantity in 1000 units; value in $1000 U

Origin and 

Commodity 

Values in 1000 dollars/Quantities in Thousands, Except Where Indicated 

2000 2001 2002 2003 2004 2

Quantity Value Quantity Value Quantity Value Quantity Value Quantity Value Quantity 

EUROPEAN UNION – 25 Unrooted Cuttings/Slips, no soil 

19,573.5 $3,817 19,162.3 $3,793 20,874.8 $3,895 27,100.9 $4,910 23,340.5 $4,945 48,687 

Other Plants, with soil 12,941.2 $3,399 14,486.2 $2,791 14,934.5 $3,430 15,463.1 $4,725 13,531 $4,155 15,023 

Trees/Shrubs, with soil 186.6 $269 545 $651 370.4 $553 269.4 $714 209.7 $610 441 

Trees/Shrubs, with soil (metric tons) 

1 $4,559 0 $0 0 $0 10 $13,164 6 $6,509 0 

Roses 286.5 $463 627 $744 818.1 $1,429 415.5 $778 294.4 $493 259 

Rhododendrons, Azaleas 90 $8 96 $12 31 $3 0 $0 0 $0 

Total (thousands) $33,077.8 $7,956 $34,916.5 $7,991 $37,028.8 $9,310 $43,248.9 $11,127 $37,375.6 $10,203 $64,410 

Total (metric tons) 1 $4,559 0 $0 0 $0 10 $13,164 6 $6,509 0 

CANADA Unrooted Cuttings/Slips, no soil 

1,675.00 $802 2,290.50 $987 3,860.70 $1,529 612.2 $240 536.5 $219 1,013 

Other Plants, with soil 258,232.80 $108,713 263,284.20 $118,760 292,453.30 $131,710 289,472.50 $137,898 272,545.30 $136,290 241,766 

Trees/Shrubs, with soil 3,162.40 $3,788 3,033.30 $3,977 3,142.50 $4,252 7,581.40 $3,969 5,635.50 $3,998 5,439 Trees/Shrubs, with soil (metric tons) 

22,409 $25,294,003 43,532 $29,382,769 29,776 $25,971,459 33,231 $27,485,040 32,847 $30,443,868 29,053 

Roses 6,609.40 $11,071 6,166.30 $12,459 6,566.00 $12,563 7,429.10 $14,950 7,496.80 $15,199 7,006 

Christmas Trees not Firs 447.7 $5,083 415.3 $4,534 377.8 $4,100 344.5 $4,105 292.4 $4,342 247 

Christmas Trees, Firs 2,063 $18,944,036 2,195 $21,618,957 2,241 $22,113,441 2,169 $23,461,596 2,015 $23,358,746 1,981 

Rhododendrons, Azaleas 665.3 $3,352 771.2 $3,665 2,153.80 $3,237 510 $2,580 528.6 $2,842 533 

Total (thousands) 272,855.6 19,076,845 388,461.8 21,763,339 431,291.1 22,270,832 441,911.7 23,625,338 428,902.1 23,521,636 396,292 

Total (metric tons) 22,409 $25,294,003 43,532 $29,382,769 29,776 $25,971,459 33,231 $27,485,040 32,847 $30,443,868 29,053 

*Data compiled by Lynn Garrett, USDA APHIS CPHST PERAL Economist 

. 

29 
Fig. 3. Locations receiving plants shipped from nurseries testing positive for Phytophthora ramorum 2004-2006 overlaid on 

30 
 

V. Pathway Assessments 

The preceding section contained an overall pest risk assessment for P. ramorum. This section 

takes information from the overall assessment and focuses it on particular pathways. Pathways 

analyzed are nursery stock (including Christmas trees for planting), wood and wood 

products, cut Christmas trees, cut foliage/flowers, greenwaste, compost, potting media, and 

soil. As in the overall assessment, risk levels are categorized as High, Medium, and Low and 

levels of uncertainty are indicated. The risk ratings for the overall and individual pathway 

assessments are summarized in a comparative risk matrix (Table 6). 

A. Consequences of Introduction 

Risk Element 1: Climate-Host Interaction 

This risk element considers ecological zonation and the interactions of P. ramorum with its hosts 

in a variety of environments with diverse biotic and abiotic conditions. When introduced into 

new areas, pests are expected to behave as they do in their native areas if the potential host plants 

and suitable climate are present. Broad availability of suitable climates and a wide distribution 

of suitable hosts are assumed to increase the impact of a pest introduction. The ratings for this 

risk element are based on models, research, and the number of United States Plant Hardiness 

Zones (USDA, 2003) which contain potential host plants and suitable climate. Because of the 

large number of hosts and climate range, the analysis of this Element applies to all pathways. 

Phytophthora ramorum has a high probability of encountering favorable climatic conditions 

throughout the ranges of potential hosts that occur in several Plant Hardiness Zones. Modeling 

of environmental conditions suggests there are many areas in the United States outside the 

quarantined areas of California and Oregon that have both favorable conditions for disease 

development and susceptible hosts (Kluza et al., 2007; Magarey et al., 2004, 2007; Smith et al., 

2002). 

The rating for the Climate-Host Interaction element is High for all pathways assessed. The 

uncertainty lies in the range of biotic and abiotic factors triggering establishment of 

P. ramorum in new areas. 

Risk Element 2: Host Range 

The risk posed by a plant pest depends on both its ability to establish a viable reproductive 

population and its potential to damage plants. This risk element assumes that the consequences 

of pest introduction are positively correlated with the pest’s host range. Aggressiveness, 

virulence, and pathogenicity may also be factors. The consequences related to host range are 

rated in accordance with the ability of the pathogen to attack a single species or multiple species 

within a single genus, a single plant family, or multiple families. 

The host range of this pathogen continues to expand though detections in the field. APHIS 

currently regulates 40 plant species and all species in five genera as proven hosts, with an 

additional 64 species listed as associated plants (Table 1) (APHIS, 2007a). The potential host 

range is also increasing, as determined through a variety of screening techniques including 

detached leaf, whole plant, and log assays (DEFRA, 2004c; Hansen et al., 2005; RAPRA, 2007; 

Tooley and Kyde, 2007). Experimental evidence indicates that several eastern forest species 

would be more susceptible than western forest species, such as in affected quarantined areas of 

31 
California and Oregon. In addition, differences in host susceptibility are documented for forest 

and nursery species and may affect disease development in new environments (DEFRA, 2004c; 

Linderman et al., 2007; Meshriy et al., 2005; Tooley et al., 2004; Tooley and Kyde, 2007). 

Nursery Stock (Including Christmas Trees for Planting) 

Nursery plants are intended for planting in the landscape. The locations of these plantings 

include commercial plantings, private residences, arboreta, large parks, and interiorscapes. 

Christmas trees are often planted in home landscapes. Pseudotsuga menziesii var. menziesii and 

A. grandis are confirmed hosts used as Christmas trees. Several nursery plants, specifically 

Camellia spp., Pieris spp., Rhododendron spp., and Viburnum spp., have already been implicated 

in the movement of P. ramorum. These four genera have been associated with repeated 

regulatory actions in North America and Europe and appear to present a greater risk for the 

pathogen’s movement (APHIS, 2005b, 2007b; COMTF, 2005; EC, 2007). 

Wood and Wood Products 

Wood and wood products can be an important pathway for the movement of P. ramorum. 

Brown and Brasier (2007) isolated P. ramorum from the xylem up to 25 mm below the phloem 

and up to 27 weeks after removal of the phloem of A. pseudoplatanus, F. sylvatica, Q. cerris, 

Q. acuta, and Q. petraea. Parke et al. (2007) found P. ramorum in xylem tissue and 

chlamydospores in xylem vessels. Phytophthora ramorum has been recovered from firewood 

after six months of storage (Shelly et al., 2005b). Sporulation has not been observed on the 

outside, intact bark of infected Quercus spp. or L. densiflorus logs (Davidson et al., 2005). 

However, the pathogen has been recovered from or observed to sporulate on various wood 

products, e.g., flooded chips of infected L. densiflorus and the flooded, cut edges of Q. agrifolia 

cankers (Davidson and Shaw, 2003). Results from log inoculation tests of P. menziesii var. 

menziesii have been inconsistent (Hansen et al., 2004). The main trunks of P. menziesii var. 

menziesii and S. sempervirens, important timber species, have not been found to be infected by 

P. ramorum (Davidson et al., 2003c) 

Cut Christmas Trees 

Pseudotsuga menziesii var. menziesii and A. grandis are grown in plantations and farmed for 

Christmas trees (COMTF, 2005). Pseudostuga menziesii var. glauca, while not a host, has 

demonstrated susceptibility to P. ramorum in controlled studies; it is native to the intermountain 

zones (Rocky Mountains) and occurs at higher elevations and has greater cold hardiness than P. 

menziesii var. menziesii. In mixed forests, P. ramorum has been found infecting understory P. 

menziesii var menziesii and small branches, needles of sprouts, and twig tips of S. sempervirens. 

Studies are underway to examine sporulation on these two hosts (Davidson et al., 2003c). 

Twenty of the conifer species tested, including many important species used as Christmas trees, 

were susceptible to P. ramorum (Chastagner et al., 2004). Some Abies spp. were highly 

susceptible. Symptoms included needle blight, a shoot blight resulting from needle infections, 

and stem lesions resulting from the growth of the pathogen from infected needles into the stem. 

Growth stage has an apparent significant effect on susceptibility (Chastagner et al., 2004). 

Cut Flowers/Foliage 

Leaves and branches of hosts such as U. californica, P. menziesii var. menziesii, and 

S. sempervirens are used in wreaths and garlands (Davidson and Shaw, 2003). Rhododendron 

and U. californica leaves can be dried for several weeks, and the pathogen is still viable after 

rehydration (Garbelotto, 2003a). Numerous hosts of P. ramorum are popular for cut flower 

32 
production, including Acer, Camellia, Hamamelis, Kalmia, Pieris, Rhododendron, Rosa, and 

Syringa (Bachmann, 2002). There are multiple areas of uncertainty, including a lack of data on 

infestation and transmission rates of P. ramorum in other host species used for cut foliage and 

flowers. For example, movement of P. ramorum in Viburnum and Rhododendron nursery stock 

is documented (APHIS, 2005b, c; COMTF, 2005), but not in cut flowers. The intended uses and 

disposal of plants for planting and internal ornamental use differ. Cut flowers and foliage are 

less likely to come into contact with live hosts, since most of this material is used for decorative 

purposes indoors and then discarded. 

Greenwaste and Compost 

An estimated 10 million tons of greenwaste infected by P. ramorum accumulate in coastal 

California each year (Garbelotto, 2003a). Greenwaste containing host material from infested 

areas may serve as a source of inoculum, especially from leaves of foliar hosts. Rhododendron 

and U. californica leaves can be dried for several weeks and the pathogen is still infectious after 

rehydration (Garbelotto, 2003a). Although it has not been demonstrated, it is postulated that 

spores could be dispersed from foliar hosts via rain-splash if open transit containers are used, or 

that infected leaves could detach and blow away (Davidson and Shaw, 2003). 

When infected wood chips, firewood, and branches are kept in a cool and moist environment, 

they can harbor viable P. ramorum for long periods (Shelly et al., 2005a, b). These substrates 

are commonly brought into commercial composting facilities (Garbelotto, 2003a). 

Municipal composting processes reduce the viability of many plant pathogens, including 

P. ramorum, due to high temperatures and enzymatic activity. Composting has been 

demonstrated to reduce P. ramorum populations below detectable levels; however, preliminary 

data suggest re-infestation of finished compost by the pathogen is possible (Swain and 

Garbelotto, 2006). 

Potting Media 

Potting media are composed of organic and inorganic matter and are intended for various uses 

both indoors and outside. Experimental evidence indicates that P. ramorum may survive and 

infect plants via potting media. Parke et al. (2004a) and Parke and Lewis (2007) found that 

P. ramorum moved through a sterile potting medium and infected Rhododendron plants. 

P. ramorum survived in Camellia leaves up to 100 days in a potting medium, even after the 

leaves were decaying (Shishkoff and Tooley, 2004), and up to 11 months on Camellia and 

Rhododendron roots buried in potting media (Shishkoff, 2007). In laboratory tests, the form of 

inoculum influenced the survival of P. ramorum in potting media, e.g., six months when 

introduced as sporangia and 12 months when introduced as chlamydospores (Linderman and 

Davis, 2006c). Phytophthora ramorum has also been recovered from potting media at an infested 

nursery (OSOS, 2004). 

Soil 

Phytophthora ramorum has been isolated seasonally from soil in hiking trails and from soil on 

hikers’ boots (Cushman and Meentemeyer, 2006; Davidson et al., 2002c; Tjosvold et al., 2002b; 

Webber and Rose, 2008). In this same study, a survey of those visitors with infested shoes 

showed that many people leaving the park were going to other parts of California, the United 

States, or Europe (Tjosvold et al., 2002b). Recovery rates of P. ramorum in areas with host 

plants was equal from soil samples collected on hiking trails and off the trails (Cushman and 

33 
 

Meentemeyer, 2006). The pathogen was only recovered from samples collected from the trails 

in two areas without hosts, suggesting human-assisted movement of the pathogen along the 

trails. In the laboratory survival tests, Linderman and Davis (2006c) inoculated several 

substrates (coir dust, composted dairy manure, fir bark, peatmoss, potting mix, alluvial sand, 

sawdust, and garden clay loam soil) with P. ramorum sporangia. The pathogen was recovered 

up to six months in coir dust, composted dairy manure, fir bark, potting mix and sawdust; five 

months in peat moss; four months in garden clay loam soil; and two months in alluvial sand. 

The rating for the Host Range Risk Element is High for the Nursery Stock, Wood and 

Wood Products, Greenwaste, Compost, Potting Media, and Soil pathways. The Cut 

Christmas Trees and Cut Flowers/Foliage pathways are rated Medium because of end use 

and disposal. The uncertainty in the ratings for this Element lies in the unknowns, e.g., the 

extent of the host range, infestation and transmission rates, and disposal methods. 

Risk Element 3: Dispersal Potential 

Pests may disperse after introduction into new areas. The dispersal potential indicates how 

rapidly and widely the pests may spread within the importing country or region and is related to 

the pest’s reproductive potential, inherent mobility, and external dispersal facilitation modes. 

Factors for rating the dispersal potential include the presence of multiple generations per year or 

growing season, the relative number of offspring or propagules per generation, any inherent 

capabilities for rapid movement, the presence of natural barriers or enemies, and dissemination 

enhanced by wind, water, vectors, or human assistance. 

The scattered pattern of sites where P. ramorum has become established suggests it has both 

natural (Hansen et al., 2002; Tjosvold et al., 2002c) and human-assisted movement (Werres et 

al., 2001). Long-distance spread may occur when strong winds, common during heavy rains 

along the California coast, move the easily detached sporangia great distances (Hansen et al., 

2002). Initial survey results in California and Oregon indicate P. ramorum is in streams and 

rivers adjacent to and far from known infested areas (Hansen et al., 2005; Murphy et al., 2006). 

Anthropogenic movement includes soil on hikers’ boots (Davidson et al., 2002c, 2005; Tjosvold 

et al., 2002b) and nursery stock (APHIS, 2005b, c). 

Nursery Stock (Including Living Christmas Trees) 

Phytophthora ramorum is a polycyclic pathogen on many nursery hosts; evidence indicates that 

inoculum production follows periods of rain and that certain foliar hosts, including 

Rhododendron and Syringa, are prolific producers of sporangia or chlamydospores or both 

(Davidson et al., 2003c). Pathogen transmission has been documented from one nursery to 

another on nursery stock. Confirmed positive sites from the trace-forward, national, and other 

survey total 176 in 21 states (APHIS, 2005a, b). While most of these were nursery finds, the total 

includes three residential finds. As of January 10, 2005, all nursery stock shipped from 

California, Oregon, and Washington is regulated to prevent movement of this pathogen (APHIS, 

2005a). In Europe, P. ramorum has been transported into a number of countries via infected 

nursery stock (Davidson and Shaw, 2003; Lilja et al. 2007; RAPRA, 2007). 

34 
 

 

 

Wood and Wood Products 

Wood and wood products can be an important pathway for the movement of P. ramorum. The 

pathogen has been recovered from or observed to sporulate on various wood products. 

Sporulation has occurred on flooded chips of infected L. densiflorus and the flooded, cut edges 

of Q. agrifolia cankers (Davidson and Shaw, 2003; Davidson et al., 2005). The pathogen has 

been recovered 3 cm into wood of Quercus spp. (D. Rizzo, unpublished data in Davidson and 

Shaw, 2003), up to 25 mm from A. pseudoplatanus, F. sylvatica, Q. acuta, Q. cerris, and 

Q. petraea (Brown and Brasier, 2007); up to 4 cm in L. densiflorus (Parke et al, 2007); and from 

firewood after six months of storage (Shelly et al., 2005a), indicating that wood products (mulch, 

firewood, chips, etc.) may be infective. Sporulation has not been observed on the outside of 

intact bark of infected Quercus spp. or L. densiflorus logs (Davidson et al., 2005). However, the 

main trunks of P. menziesii var. menziesii and S. sempervirens, important timber species, have 

not been found to be infected by P. ramorum (Davidson et al., 2003c) and so logs, lumber, and 

other wood products of these species are not regulated. 

There is uncertainty with this pathway. Data on infestation and transmission rates of 

P. ramorum in wood products indicate that the recovery of the pathogen is low. When coupled 

with the uncertainties about P. ramorum survival, especially chlamydospores, these rates may be 

deceptively low. 

Cut Christmas Trees 

Pseudotsuga menziesii var. menziesii, a host of P. ramorum, is native to the Sierra Nevada and 

coastal mountains of California, Oregon, Washington, and British Columbia; it is grown in 

plantations and farmed for Christmas trees. P. ramorum infects the small branches of 

P. menziesii var. menziesii and the small branches and needles of S. sempervirens. Studies are 

underway to examine sporulation on these two hosts (Davidson et al., 2003c). In 2004, 665 

Christmas tree plantations in Oregon and 100 in Washington were surveyed and found negative 

for P. ramorum (COMTF, 2004b). Twenty of the conifer species tested, including many 

important species used as Christmas trees, were susceptible to P. ramorum (Chastagner et al., 

2004, 2006b). Some Abies spp. were highly susceptible in laboratory tests. Symptoms included 

needle blight, a shoot blight resulting from needle infections, and stem lesions where the 

pathogen infecting needles grew into the stem. Growth stage had a significant effect on 

susceptibility. 

Cut Flowers/Foliage 

Leaves and branches of hosts such as U. californica, P. menziesii var. menziesii, and 

S. sempervirens are used in wreaths and garlands. Some of these plants are grown within the 

regulated counties in California and have been sold throughout the United States. Even without 

sporulation, fir wreaths and Christmas trees could serve as an infection pathway if hyphae were 

able to grow from infected branch tips and needles (Davidson and Shaw, 2003). 

Additional host species are used for cut flowers and foliage, including Rhododendron, Kalmia, 

Camellia, and Syringa on which P. ramorum can effectively produce spores (Beales et al., 

2004b; Davidson et al., 2003c; DEFRA, 2004c; Parke et al., 2002a). Although there are data for 

the movement of P. ramorum in these hosts as nursery stock, there are no data for cut flowers. 

These products may be capable of disseminating the pathogen, but their intended use and 

disposal are principally indoors, reducing the likelihood that they will contact hosts in a new 

environment. 

35 
Greenwaste/Compost 

Greenwaste containing host material from infested areas may be a source of inoculum, especially 

from leaves of foliar hosts (Davidson and Shaw, 2003). Even green material dried for several 

weeks can be problematic because some plant tissue, such as Rhododendron leaves, will 

sporulate upon wetting (Garbelotto, 2003a). Although it has not been demonstrated, it is 

postulated that spores could be dispersed from foliar hosts via rain-splash during transit in open 

containers, or that infected leaves could detach and blow away (Davidson and Shaw, 2003). 

Composting can reduce available inoculum from P. ramorum infected materials (Aveskamp and 

Wingelaar, 2006; Garbelotto, 2003a; Swain et al., 2005, 2006), but is not equally effective on all 

materials (Swain et al., 2005). Municipal composting processes reduce the viability of many 

plant pathogens, including P. ramorum, due to high temperatures and enzymatic activity. 

Composting reduced P. ramorum populations below detectable levels; however, preliminary data 

suggested reinfestation of finished compost is possible (Garbelotto, 2003a; Swain and 

Garbelotto, 2006; Swain et al., 2006). 

Potting Media 

The Oregon Department of Agriculture has detected P. ramorum in nursery stock, potting media 

containing compost, and plants in a landscape in Columbia County. This prompted the Oregon 

Secretary of State to implement an Emergency Quarantine Order in July 1, 2004 to prevent the 

movement of potting media and compost (OSOS, 2004). 

Parke et al. (2006b, 2007) demonstrated transmission of P. ramorum from infested potting 

medium to Rhododendron plants under greenhouse and laboratory conditions. Linderman and 

Davis (2005, 2006a, c) compared P. ramorum with other Phytophthora species in a variety of 

soil-less potting media (river sand, Douglas-fir bark, coir, sphagnum peat, redwood sawdust, a 

bark-peat-pumice potting mix), dairy compost, and garden soil. The pathogen was detected for 

six months from all substrates amended with sporangia or chlamydospores in vermiculite but not 

with infected leaf inoculum. P. ramorum sporangia survived best in peat moss, the potting mix, 

coir, and Douglas fir bark, and poorest in sand and soil. These results indicate that 

P. ramorum survives very well in potting mix components and soil as culture-produced 

sporangia or chlamydospores. 

Soil 

Inoculum has been isolated seasonally from soil in hiking trails and from soil on hikers’ boots 

(Davidson et al., 2002c; Tjosvold et al., 2002b). In this same study, a survey of those visitors 

with infested shoes showed that many people leaving the park were going to other parts of 

California, the United States, or Europe (Tjosvold et al., 2002b). The concern for soil and litter 

movement by equipment has prompted California authorities to request that vehicles and other 

equipment, including tents and shoes, be washed prior to leaving an established area. 

Phytophthora ramorum has been recovered, albeit at low levels, from a variety of unprocessed 

and processed wood products (Shelly et al., 2005b). Soil on felled trees or logging equipment 

from infested forests may also contain spores (Davidson and Shaw, 2003). Recovery rates of 

P. ramorum in areas with host plants was equal from soil samples collected on hiking trails and 

off the trails. The pathogen was only recovered from samples collected from the trails in two 

areas without hosts, suggesting human-assisted movement of the pathogen along the trails 

(Cushman and Meentemeyer, 2006). Fichtner et al. (2007a) reported that it is difficult to detect 

chlamydospores using current baiting methods, and indicated an underestimation of the amount 

36 
of inoculum present in the soil. Rhododendron leaf baits were demonstrated to be superior to 

pear baits for detection of sporangia; neither bait detected chlamydospores. In addition, soilincubated inoculum exhibited greater than 60% survival at the end of summer and also supported 

elevated chlamydospore production, which may provide a reservoir of inoculum for the fall 

disease cycle (Fichtner et al., 2007a). 

The rating for the Dispersal Potential Element is High for the Nursery Stock, Wood and 

Wood Products, Greenwaste/Compost, Potting Media, and Soil pathways. The risk for Cut 

Foliage/Flowers and Cut Christmas Trees is Medium because of intended use, i.e., indoors. 

However, the uncertainty is the final disposition, which could be indoors in trash or outside 

in compost or greenwaste. 

Risk Element 4: Economic Impact 

Introduced pests cause a variety of direct and indirect economic impacts, such as reduced yield, 

reduced commodity value, loss of foreign or domestic markets, and non-crop impacts. Factors 

considered during the ranking process included the following: effect on yield or commodity 

quality; plant mortality; ability to act as a disease vector; increased costs of production, including 

pest control costs, lower market prices, effects on market availability, increased research or 

extension costs, or reduction in recreational land use or aesthetic value; ability of the pest to 

attack the hosts or products with significant commercial value, to directly cause tree mortality, or 

to predispose the host to mortality by other organisms; impact of the pest on the value of the 

affected host, e.g., by lowering its market price, increasing cost of production, maintenance, or 

mitigation, or reducing value of property where it is located; and lack of effective control 

measures. 

The economic impact of each pathway is addressed below. Losses in real estate value and costs 

of removal and disease management are estimated to be about $100 million/year (Stipes and 

Campana, 1981). In addition, plant pathogens of forest plants cause the loss of approximately 

9%, or $7 billion, of forest products each year (Hall and Moody, 1994; USBC, 1998). The 

proportion of introduced plant pathogens in forests is similar to that of introduced insects (about 

30%); thus, approximately $2.1 billion in forest products are lost each year to non-indigenous 

plant pathogens in the United States. In addition, tourism can be affected, as visitors to parks 

and forests may find that access to selected areas is restricted during certain seasons to prevent 

the pathogen’s movement, or to protect visitors from falling limbs from trees killed by P. 

ramorum (COMTF, 2004a). When visitors are requested or required to take precautions to 

prevent movement, park and forest staff maybe required to provide educational information, staff 

cleaning areas, and provide appropriate supplies and equipment to remove soil from shoes and 

vehicles. 

Nursery Stock (Including Living Christmas Trees and All Propagative Material) 

Nursery crops are woody perennial plants such as ornamental trees, shrubs, and vines that are 

primarily used for landscaping. In 2006, the U.S. domestic production of nursery crops was 

valued about $12.9 billion. Imports for these crops were $341 million and exports were $287 

million (Jerado, 2007). Lost in nursery stock from regulatory actions in the state of Washington 

in 2004 and 2005 was over $400,000, and this value does not include labor or other costs 

associated with the destruction of the plants and eradication efforts at the nurseries involved 

(Dart and Chastagner, 2007). 

37 
The presence of P. ramorum has resulted in restrictions in the foreign and domestic trade of 

nursery stock. Australia, Canada, Korea, New Zealand, the European Union, and Switzerland 

have placed restrictions on the movement of affected plants and plant parts from the United 

States (EXCERPT, 2007; Rizzo and Garbelotto, 2003). In addition, the United States has placed 

restrictions on movement of propagative material from Europe (Aley, 2007). 

Wood and Wood Products 

Thousands of Quercus and L. densiflorus trees have died following infection by this pathogen, 

requiring expensive removal in certain settings, more intensive fire management in others, and 

limited access to parts of parks and forests (COMTF, 2004c). Economic losses from removal of 

infected Quercus trees may be partially offset by utilization of the material for wood products 

(Shelly et al., 1996). The presence of P. ramorum has resulted in restrictions in foreign and 

domestic trade. Canada, Korea, Australia, New Zealand, and the European Union have placed 

restrictions on the movement of affected plant and plant parts from the United States 

(EXCERPT, 2007; Rizzo and Garbelotto, 2003). Should P. ramorum become established in 

other U.S. hardwood forests, the potential economic threat to commercial timber production 

exceeds $30 billion (Kliejunas, 2003). 

Cut Christmas Trees 

The U.S. cut Christmas tree industry had a wholesale value of $520 million in 2003 (Jerado, 

2004). Oregon leads with a total production of $158 million (Jerado, 2004) and markets 

throughout the United States, Canada, and Mexico (OASS, 2004). Washington and California 

follow with values of $60 and $10.4 million, respectively (Jerado, 2004). A major Christmas 

tree species, P. menziesii var. menziesii, is a host of P. ramorum. Chastagner et al. (2004) found 

other important species susceptible in laboratory trials, and other species have been found 

naturally infected, e.g., Abies grandis and A. magnifica (Table 1.) 

Cut Flowers/Foliage 

U.S. production exceeded $406 and $542 million respectively for cut flower and foliage sales 

(Jerado, 2007). Many of the species surveyed and listed by National Agricultural Statistics 

Service (NASS, 2007) were not hosts of P. ramorum, but there is an increase in flower 

production of woody ornamentals and many of these plants are hosts for the pathogen, including 

Acer, Camellia, Hamamelis, Kalmia, Pieris, Rhododendron, Rosa, and Syringa (Bachmann, 

2002). 

Greenwaste/Compost 

A major economic issue for quarantined counties in California is appropriate disposal of 

P. ramorum-infested or contaminated greenwaste. It is estimated that about 10 million tons of 

infected greenwaste are accumulating in quarantined counties in California per year (Garbelotto, 

2003a). This is complicated by the fact that only 50% of this material can go into landfills 

(COMTF, 2005). 

Twenty-nine of 143 nurseries questioned by State officials or industry representatives in the 

quarantined counties of California indicated they would suffer a financial loss if they could no 

longer use native soil or local compost (Jordan, 2003). 

38 
Potting Media and Soil 

The pathogen was detected in potting media at an infested nursery in Oregon (OSOS, 2004). 

Subsequently, Oregon requires potting media used at certified nurseries to be tested. There is 

experimental evidence that river sand, Douglas-fir bark, coir, sphagnum peat, redwood sawdust, 

and a bark-peat-pumice potting mix are capable of harboring P. ramorum (Linderman and Davis, 

2006a, c). 

Twenty-nine of 143 nurseries questioned by State officials or industry representatives in the 

quarantined counties of California indicated they would be affected financially if they could no 

longer use native soil or local compost (Jordan, 2003). 

The Economic Impact rating for all pathways is rated High. Uncertainty stems from 

unknowns regarding the extent of the host range, the restricted movement imposed by the 

quarantines, the length of pathogen survival in various pathways, and the value of these 

products on the open market. 

Risk Element 5: Environmental Impact 

The ratings for this risk element are based on three aspects: the potential of the pest to disrupt 

native ecosystems and habitats within its current geographic range, the need for additional 

chemical or biological control programs, and the potential of the pest to directly or indirectly 

impact species listed as Threatened or Endangered (50 CFR §17.11-12). When a pest is known 

to infest or infect other species within the same genus, and host specificity data do not exist with 

the listed plant, then the listed plant is assumed to be a potential host. 

In forests, more than 20 non-indigenous species of plant pathogens attack woody plants 

(Liebhold et al., 1995). Two of the most destructive plant pathogens are Cryphonectria 

parasitica and Ophiostoma ulmi, the causal agents of chestnut blight and Dutch elm disease, 

respectively. Before the introduction of chestnut blight, approximately 25% of eastern U.S. 

deciduous forest consisted of American chestnut trees (C. dentata) (Liebhold et al., 1995). 

These trees have all but disappeared. In urban and forest environments, species and cultivars of 

Ulmus have been destroyed by O. ulmi. Environmental costs associated with prevention, 

eradication, or suppression of this pathogen include indirect ecological consequences 

(perturbations of hydrological cycles, e.g., flood control and water supply, waste assimilation, 

nutrient recycling, conservation and regeneration of soils, crop pollination) and must take into 

account both current-use value and future-use values. 

Quercus species are the most important and widespread of the hardwood trees in the North 

Temperate Zone (Pavlik et al., 1991, as cited in Kliejunas, 2003). These woodlands yield 

important benefits, e.g., water and watershed protection, grazing, wildlife food and habitat, 

recreation, and wood products (Monahan and Koenig, 2006; Thomas, 1997); are known for their 

scenic beauty; and contribute to tourism and high property values. The loss of keystone Quercus 

species in these forests would be detrimental to forest health. In addition, the effects on rare and 

endangered plant species in these regions are unknown. Phytophthora ramorum is expected to 

cause significant direct environmental effects such as extensive ecological disruption or largescale reduction of biodiversity. This pathogen has already caused environmental damage with 

the death of thousands of Quercus and Lithocarpus trees. The loss of one particular oak species, 

Q. agrifolia, has been shown to negatively affect the populations of five California bird species 

39 
(Monahan and Koenig, 2006). Barrett et al. (2006) indicated that dozens of wildlife species 

would be negatively affected by the loss of L. densiflorus, Q. kelloggii, and Q. agrifolia and the 

associated loss of food, nesting, and den sites. 

A number of genera on the APHIS List of Proven Hosts and Associated Plants have species on 

the U.S. Fish and Wildlife Service Threatened and Endangered Species List (USFWS, 2007). 

These are Arctostaphylos confertiflora, A. glandulosa ssp. crassifolia, A. hookeri var. ravenii, 

A. morroensis, A. myrtifolia, A. pallida, Prunus geniculata, Q. hinckleyi, and R. chapmanii. 

Although the rate of introduction may vary with each pathway, the impact on the environment is 

the same. Phytophthora ramorum can move in nursery stock (APHIS, 2005b; Bulluck et al., 

2006), wood and wood products (Shelly et al., 2005b), cut Christmas trees (Chastagner et al., 

2004), cut flowers/foliage (Davidson et al., 2003c; DEFRA, 2004c; Parke et al., 2002a), 

greenwaste/compost (Garbelotto, 2003a; Swain et al., 2005, 2006), potting media (Linderman 

and Davis, 2006a, c; Parke et al., 2006b), and soil (Davidson et al., 2002c; Davidson and Shaw, 

2003; Tjosvold et al., 2002b). All of the pathways present a potential risk of contaminating the 

environment with P. ramorum. 

The Environmental Impact rating for all pathways is High. The uncertainty lies with the 

difficulty in producing estimates for the costs of P. ramorum that address all of the relevant 

ecological components. These include: (1) the environmental costs of prevention, 

eradication, or suppression due to herbicide use; (2) the effects on endangered species; and 

(3) the indirect ecological consequences (changes in locally important ecological processes 

such as perturbations of hydrological cycles, e.g., flood control and water supply, waste 

assimilation, nutrient recycling, conservation and regeneration of soils, and crop 

pollination and habitat destruction). 

B. Likelihood of Introduction to New Areas in the United States 

Risk Element 6: Pest Opportunity (Survival and Access to Suitable Habitat and Hosts) 

Subelement 1: Entry Potential 

The rating for this risk element is based on the volume of domestic shipments and imports from 

Europe and Canada. This rating is also based on the likelihood that the pathogen will survive 

post-harvest treatments and shipping conditions. Live plants are grown, shipped, and sent to 

areas conducive to their survival. Handling of plant products may not be detrimental to the 

survival of P. ramorum. Although not handled as gently as live plants and cut flowers/foliage, 

other infested plant products such as logs, lumber, wood chips, and firewood still harbor the 

pathogen and present a pathway for introduction into new areas. Living plants are not likely to 

receive post-harvest treatments such as irradiation, methyl bromide, or steam sterilization 

because there is no “harvest” of the commodity, and the types of treatments that would kill the 

pests are also likely to kill the plants. In addition, the presence of potting media or soil requires 

specific testing to ensure the efficacy of any proposed post-harvest treatments (Jarvis, 1992). 

General transport conditions for potted plants range from 10-18°C and 85-90% relative humidity 

(McGregor, 1987). 

40 
 

Nursery Stock (Including Living Christmas Trees) 

Phytophthora ramorum is likely to survive in the plant host during transportation. This was 

demonstrated recently when infected nursery stock in 21 states was traced to infested nurseries in 

California. In Europe, P. ramorum was introduced to Majorca, Spain via a shipment of infected 

rhododendrons, and many of the infections found in nurseries in Europe could be traced to plant 

transport from other nurseries (Davidson and Shaw, 2003; Lilja et al., 2007; RAPRA, 2007; 

Rytkönen et al., 2007). Chlamydospores are often formed inside host tissue (Parke and Lewis, 

2007; Pogoda and Werres, 2004), and are unlikely to be dislodged during standard harvesting, 

handling and shipping operations. Phytophthora ramorum has survived up to six months in 

greenhouse conditions (Linderman and Davis, 2006a, c), overwintered in the United Kingdom 

(DEFRA, 2004c), and over-summered in the United States (Fichtner et al., 2006a, b, 2007a). 

The biology of chlamydospores of P. ramorum and their epidemiological role is still under 

investigation, but chlamydospores of other Phytophthora species can survive for up to five years 

(Erwin and Ribeiro, 1996). Detached Rhododendron and U. californica leaves still produced 

sporangia several weeks after drying (Garbelotto, 2003a). In addition to movement with the 

aerial portions of the host, there is laboratory evidence that the pathogen may move in potting 

media and evidence of root infection in nursery stock (Linderman and Davis, 2006a, 2006c; 

Parke et al., 2004a; Parke and Lewis, 2007; Shishkoff, 2007). 

Wood and Wood Products, Cut Christmas Trees, Cut Flowers/Foliage 

This pathogen has been detected and isolated from bark, cambium, and xylem and is usually 

limited to a depth of 2.5 cm in Quercus (Brown and Brasier, 2007) and as deep as 4 cm in L. 

densiflorus (Parke et al., 2007). Chlamydospores are often formed inside host tissue (Parke et al., 

2003; Pogoda and Werres, 2004) and are unlikely to be dislodged during standard harvesting, 

handling, and shipping operations. Phytophthora ramorum has survived up to six months in 

greenhouse conditions (Linderman and Davis, 2006a, c), overwintered in the United Kingdom 

(DEFRA, 2004c), and over-summered in the United States (Fichtner et al., 2006b, 2007a). Much 

of the biology of its chlamydospores is still under investigation, but chlamydospores of other 

Phytophthora species can survive for up to five years (Erwin and Ribeiro, 1996). 

Greenwaste/Compost, Soil, Potting Media 

Phytophthora ramorum has been detected from greenwaste (Shelly et al., 2005a), compost 

(Garbelotto, 2003a), soil (Tjosvold et al., 2002b), and potting media (Linderman and Davis, 

2006a, c; Parke et al., 2006b; Shishkoff, 2007). Spores of P. ramorum have been detected on 

hikers’ shoes and on the tires of mountain bikes and vehicles used on dirt roads or trails in 

California (Tjosvold et al., 2002b). Linderman and Davis (2006a, c) compared P. ramorum with 

other Phytophthora species in a variety of media (river sand, Douglas-fir bark, coir, sphagnum 

peat, redwood sawdust, a bark-peat-pumice potting mix, a dairy compost, and a garden soil) and 

found that the pathogen was detected for six months from all substrates. 

The risk rating for the Entry Potential is High for all pathways except compost, which is 

rated Medium. Uncertainty factors include lack of data on infection and pathogen survival 

rates for most products, especially cut flowers and foliage; long-term survival in 

greenwaste, compost, potting media, and soil; and propagules present in wood and wood 

products. 

41 
Subelement 2: Establishment and Spread Potential 

Phytophthora ramorum is a polycyclic pathogen; evidence indicates that inoculum production 

follows periods of abundant rainfall, and P. ramorum produces large numbers of sporangia, 

chlamydospores, or both on certain foliar hosts (Davidson et al., 2003a, 2005). Phytophthora 

ramorum has an optimum temperature range of 18°-25°C (DEFRA, 2004c; Werres et al., 2001) 

and survives temperatures as low as -9°C (DEFRA, 2004c). Suitable hosts must be available to 

establish and sustain a pest population, and there must be a mechanism for the pathogen to reach 

these hosts. Both natural and human-assisted factors aid in the dispersal of P. ramorum 

(Davidson et al., 2003a, b; Hansen et al., 2002). The host range of this pathogen has expanded 

and currently attacks 70 genera in 35 plant families (Table 1) (Brasier et al., 2002; Hansen et al., 

2005; Tooley and Kyde, 2003, 2007; Tooley et al., 2004). Many of these hosts are widely 

distributed in the United States, and conducive climatic conditions are prevalent along the East 

and West Coasts. Modeling of environmental conditions suggests there are several areas in the 

United States outside of quarantined zones that have both favorable conditions for disease 

development and susceptible hosts (Kluza et al., 2007; Magarey et al., 2004, 2007). 

The pathogen is established in forests in fourteen counties in California and one county in 

Oregon (APHIS, 2007b) and has been detected from limited established plantings of ornamental 

shrubs and trees in Europe (DEFRA, 2006; EPPO, 2004; RAPRA, 2007). Newly established 

populations in forests or other natural environs may go undetected for many years owing to their 

cryptic nature, concealed activity, slow development of damage symptoms, or misdiagnosis 

(Rizzo et al., 2002b). However, survey and diagnostic methods have improved, thereby 

increasing the likelihood of detecting the pathogen. Eradication is currently not feasible for 

certain forest situations, but is being attempted in Curry County, Oregon (Goheen et al., 2002b; 

Hansen and Sutton, 2006; Kanaskie et al., 2008) and in garden settings in the United Kingdom. 

Six years after initial eradication efforts, P. ramorum is still being found in native soil and 

streams in Curry County, Oregon (Kanaskie et al., 2008; Prospero et al., 2007). Although 

eradication was not considered feasible, suppression efforts are underway in Humboldt County, 

California (COMTF, 2005). 

Nursery Stock (Including Living Christmas Trees) 

Many of the hosts on the regulated and associated host lists are major nursery and/or 

forest/understory species. There is contiguous distribution of hosts, potential hosts, and 

favorable conditions along the East and West Coasts of the United States (Magarey et al., 2004, 

2008). Phytophthora ramorum has been detected and eradicated in nursery stock shipped from 

California to 21 other States. This pathogen has also been detected in nursery stock in many 

European countries, and from a few established plantings on Rhododendron and various tree 

hosts (EPPO, 2004). In addition, in infested nurseries soil or mulch in the pots of rhododendron 

plants, other host plants, and even non-host plants that appear healthy may contain spores of 

P. ramorum (Davidson and Shaw, 2003). Phytophthora ramorum has also been isolated from 

irrigation water from an infested rhododendron nursery (Tjosvold et al., 2002c). In addition, 

P. ramorum has been detected downstream from nurseries with infested nursery stock (APHIS, 

2007d). 

Wood and Wood Products 

Phytophthora ramorum has been recovered from chips (Davidson et al., 2003b) and the inner 

bark and xylem (Brown and Brasier, 2007) of hardwood species, suggesting that when the inner 

bark is exposed, as in the debarking process, and free water is present, the pathogen can 

42 
 

sporulate on the exposed surfaces. Sporulation was stimulated in baiting trials when inoculated 

“logs” were kept at 12°C prior to baiting (Garbelotto, 2002) and has been recovered from 

firewood stored for six months (Shelly et al., 2005a). Tubajika et al. (2008) demonstrated that 

heat treating naturally and artificially inoculated wood rounds and boards to 56 °

C for 30 minutes 

may not have been adequate to kill the pathogen. APHIS does not regulate the movement of 

conifer wood or wood products (APHIS, 2007b). 

Cut Foliage, Flowers, and Christmas Trees 

Phytophthora ramorum readily sporulates on U. californica leaves under moist, temperate 

conditions (Davidson et al, 2003a); chlamydospore formation has also been observed. In a 

laboratory study, Linderman and Davis (2007a) found varying degrees of infection and 

sporulation by P. ramorum on all species, cultivars, and hybrids of Camellia. Chastagner et al. 

(2008) found P. ramorum on flowers of U. californica and flower peduncles of Phoradendron 

serotinum ssp. macrophyllum; Tjosvold et al. (2006b) reported infection of Camellia flower 

buds. This pathogen infects small branches of P. menziesii var. menziesii and small branches and 

needles of S. sempervirens. In 2004, 665 Christmas tree plantations in Oregon and 100 in 

Washington were surveyed and found negative for P. ramorum (COMTF, 2004b). Twenty of 

the conifer species tested, including many important species used as Christmas trees, were 

susceptible to P. ramorum (Chastagner et al., 2004). Cut flowers and foliage are less likely to 

come into contact with live hosts because much of the discarded material will end up in landfills, 

whereas discarded Christmas trees are more likely to end up as greenwaste. 

Greenwaste/Compost/Potting Media/Soil 

Phytophthora ramorum has been detected from greenwaste (Shelly et al., 2005a), compost 

(Garbelotto, 2003a), and potting media (Parke et al., 2006b). Greenwaste containing host 

material from infested areas may serve as a source of spores, especially leaves of foliar hosts 

(Davidson and Shaw, 2003). Green material dried for several weeks, such as rhododendron 

leaves, will still sporulate upon wetting (Garbelotto, 2003a). Although it has not been 

demonstrated, it is likely that spores could be dispersed from foliar hosts via rain-splash during 

transit in open containers, or that infected leaves could detach and blow away (Davidson and 

Shaw, 2003). Linderman and Davis (2006a, c) compared the survival of P. ramorum with other 

Phytophthora species in a variety of media (river sand, Douglas-fir bark, coir, sphagnum peat, 

redwood sawdust, a bark-peat-pumice potting mix, a dairy compost, and a garden soil) and found 

that the pathogen was recovered from all substrates for six months. 

Recovery rates of P. ramorum in areas with host plants were equal from soil samples collected 

on and off hiking trails. The pathogen was only recovered from samples collected from the trails 

in two areas without hosts, suggesting anthropogenic movement of the pathogen along the trails 

(Cushman and Meentemeyer, 2006). Fichtner et al. (2007a) indicate current baiting techniques 

can underestimate the amount of inoculum present in the soil. 

43 
 

The risk rating for Establishment and Spread is High for Nursery Stock, Wood and Wood 

Products, Greenwaste, Compost, Potting Media, and Soil. The risk is Medium for Cut 

Christmas Trees because the negative detections in nursery surveys show a lack of 

association with the pathway. Cut Flowers and Foliage are also rated Medium because the 

intended use does not put them into contact with suitable hosts in suitable environments. 

There is uncertainty in ratings for Cut Christmas trees and Cut Flowers and Foliage 

because the species used are susceptible. 

Subelement 3: Detection Potential 

Species of Phytophthora, such as P. ramorum, are difficult to detect at the ports–of-entry, where 

visual inspection is the primary method of detection; Phytophthora spp. have only been detected 

seven times since 1985 (PPQ, 2007a). However, Brown and Brasier (2007) have used ELISA to 

detect species of Phytophthora in the field; this may have applicability at ports-of-entry. Other 

pathogens and environmental conditions can elicit the same symptomology in foliar and dieback 

hosts. Two new Phytophthora species, P. nemorosa and P. kernoviae, induce similar cankers on 

trees and were found as a result of field analyses for P. ramorum. P. nemorosa occupies a 

similar ecological niche to P. ramorum in the United States (Hansen et al., 2004), and 

P. kernoviae occupies a similar niche in the United Kingdom (Brasier et al., 2005; DEFRA, 

2004d). Eradication efforts at nurseries and in forests are not always successful. Soil still 

harbored P. ramorum three years after initial eradication efforts in Curry County, Oregon 

(Hansen et al., 2005), and the pathogen resurfaced at nurseries in the United States and the 

United Kingdom even after prescribed control measures had been completed (APHIS, 2005b; 

DEFRA, 2005b). 

Isolation techniques, including direct plating and baiting, are used to detect the pathogen in plant 

tissues, soil, and water. The efficacy of these techniques varies with season and host (Davidson 

et al., 2002c; Fichtner et al., 2007a). Molecular detection techniques include ELISA (at the 

genus level), AFLP, and a variety of PCR protocols. A real-time PCR method is currently being 

used for regulatory purposes in both the United States and the United Kingdom. The ITS DNA 

analysis does not always distinguish P. ramorum from P. lateralis; however, multiplex methods 

can increase sensitivity. The possibility of latent infections is a concern. 

Newly established populations may go undetected. The disease was first noted in California in 

1995 (Garbelotto et al., 2001); researchers suggest the pathogen was introduced at least five 

years before the first detection (Rizzo and Garbelotto, 2003). 

Nursery Stock (Including Living Christmas Trees), Cut Foliage/Flowers, Cut Christmas 

Trees 

Visual diagnosis is still typically the first step in the detection of P. ramorum and can be 

complicated by other factors. For example, environmental conditions and other pathogens 

produce similar symptoms (Davidson et al., 2003b), and fungicides commonly used to control 

other Phytophthora species on rhododendron may mask symptoms of P. ramorum (Davidson 

and Shaw, 2003). In addition, in infested nurseries soil or mulch in the pots of Rhododendron 

plants, other host plants, and even non-host plants that appear healthy may contain spores of P. 

ramorum (Davidson and Shaw, 2003; Parke et al., 2007; Shishkoff, 2007) and be a source for reinfestation (DEFRA, 2005b). Chastagner et al. (2006a) reported that the application of contact 

fungicides in laboratory trials did not limit the recovery of P. ramorum from inoculated conifer 

44 
hosts, although growth was slower. There are also recent reports of asymptomatic infection and 

sporulation (Denman et al., 2008; Vettraino et al., 2007). 

Wood and Wood Products 

Detection methods for assessing wood products present unique challenges. Direct isolation on a 

semi-selective medium or baiting has been used to recover the pathogen from symptomatic wood 

and bark. The efficacy of these methods depends on the host and time of year. Isolation 

frequencies from wood tend to be lower than from other plant parts. Recovery was increased by 

taking plates of the semi-selective medium (PARP) to the field; however, 60% of the samples 

were negative (Storer et al., 2002). The pathogen could not be isolated from wood chips after air 

drying for two weeks (Swain et al., 2002), but lack of isolation is not definitive evidence that the 

pathogen is devitalized. The most sensitive detection method, PCR, detects the presence of the 

DNA, but does not indicate the viability of the pathogen. Recently, Brown and Brasier (2007) 

were successful at detecting several Phytophthora species, including P. ramorum, in wood using 

direct plating (within 4–24 hours post-collection and storage of 4-10oC) isolation and lateral flow 

ELISA kits. 

Greenwaste/Compost, Soil, and Potting Media 

Fichtner et al. (2006a, 2007a) found that current soil baiting techniques are adequate to detect 

sporangia but not chlamydospores in soil and thereby underestimate the amount of inoculum 

present. The same baiting techniques are used to recover P. ramorum from greenwaste, 

compost, and potting media. 

The risk rating for Detection Potential is High for all pathways. The sensitivity and 

specificity of these methods vary with season, host, host part, and pathogen propagule. 

C. Pest Risk Potential 

The overall risk presented by P. ramorum is High due to the number of pathways moving the 

pathogen and the associated uncertainties, e.g., long-term viability of infective propagules, 

difficulty in detection of the propagules, lack of definitive host range, and means of natural 

movement. Research is needed on: (1) factors inducing germination of chlamydospores; (2) 

improved detection protocols; (3) improved mitigation measures; (4) temperature requirements 

for survival of propagules in various sources, e.g., soil, wood; (5) risk associated with various 

species and hybrids of plants for planting, e.g., Christmas trees (cut and uncut), cut flowers and 

cut foliage; (6) screening for more potential hosts, including products and propagative material 

of vegetable, fruit, and nut crops; (7) natural dispersal, especially animal-aided and aerial 

dispersal; and (8) the origin and geographic distribution of Phytophthora ramorum. 

45 
 

 

 

Table 6. Comparative risk matrix for Phytophthora ramorum assessment and selected unmitigated pathways. 

Risk Element/ 

Subelement 

Organism 

Assessment 

Pathways 

Nursery 

stock 

Wood/Wood 

Products 

Cut 

Christmas 

Trees 

Cut 

Flowers/ 

Foliage 

Greenwaste/ 

Compost 

Potting 

Media Soil 

Consequences of Introduction 

Climate/Host 

Interaction High High High High High High High High 

Host Range High High High Medium Medium High High High 

Dispersal Potential High High High Medium Medium High High High 

Economic High High High High High High High High 

Environment High High High High High High High High 

Likelihood of Introduction 

Pest Opportunity 

Entry Potential 

Spread/Establishment 

Detection Potential 

High High High High High High High High 

High High High Medium Medium High High High 

High High High High High High High High 

High High High High High High High High 

Risk Potential High High High High High High High High 

VI. Mitigation Measures 

A. Introduction 

The risks associated with the importation and domestic movement of hosts and products from 

hosts of P. ramorum from infested areas without specified growing, inspection, and certification 

requirements were analyzed to be High. A risk potential of High necessitates the implementation 

of appropriate mitigation measures. 

Traditional regulatory mitigation measures for pests and plant pathogens consist of exclusion, 

containment, suppression, and eradication (Kahn, 1991). Where specific efficacies were not 

known for P. ramorum, they were deduced from the biology and management of other 

Phytophthora spp. Diagrams for the foliar host (Fig. 4), canker host (Fig. 5), soil (Fig. 6), and 

dormancy phase (Fig. 7) include points where mitigation measures may be applied. Rizzo et al. 

(2005) reviewed available research and suggested management options. 

It is difficult to design management strategies for forests (Rizzo et al., 2005). Disease 

management requires an understanding of forest ecology and pathogen biology and ecology. 

Large scale management efforts have met with varying levels of success (Rizzo et al., 2005). 

Clear-cutting was attempted to slow the spread of chestnut blight (Cryphonectria parasitica) 

(Anagnostakis, 1987); removal of alternate host material for control of white pine blister rust 

(Cronartium ribicola) (Kinloch, 2003); sanitation programs for Dutch elm disease (Ophiostoma 

ulmi, O. novo-ulmi) in North America and Europe, P. cinnamomi in Australia, and P. lateralis in 

Oregon and California (Hansen et al, 2000; Hardy et al., 2001); and fungicides to reduce the 

spread of P. cinnamomi in Australia (Hardy et al., 2001). 

The divergent goals of various stakeholder groups add to the complexity of managing 

P. ramorum in forests. Where timber production is not a major goal, management has been 

directed toward watersheds, fuel load, wildlife, and aesthetics (Rizzo et al., 2005). Where timber 

production is a goal, management plans must also incorporate riparian preservation and 

46 
 

endangered species concerns. Ultimately, any forest management strategy must integrate 

prevention, treatment, restoration, and conservation (Rizzo et al., 2005). 

Prevention of human-mediated spread has been focused, nationally and internationally, on 

quarantines on nursery plants and plant products (APHIS, 2005). There are reports of disease 

outbreaks at the urban-wildland interface associated with the planting of ornamental 

rhododendrons in California (Rizzo et al., 2005). Similar associations have been observed in 

Europe with Rhododendron planted near tree hosts (Brasier et al., 2004). Other pathways for 

human-mediated transport include soil, green waste, and stream water (Cushman and 

Meentemeyer, 2006; Davidson et al., 2005; Garbelotto, 2003a; Tjosvold et al., 2002b). 

The following portion of the document contains an overview of the mitigation measures in place 

for P. ramorum, as well as mitigation approaches that may be used to address the major 

pathways identified for its movement. The pathways are nursery stock, Christmas trees, cut 

flowers and foliage, wood and wood products, greenwaste, compost, soil, and potting media. 

B. Regulatory Measures 

Exclusion 

Exclusion of P. ramorum is facilitated by large geographical barriers. The caducous sporangia 

and zoospores are easily dispersed, locally, in rain events, and have been postulated to move long 

distances by significant weather events (Hansen et al., 2002). Sporangia of other Phytophthora 

species, i.e., P. infestans, do not survive long-distance dispersal because viability is decreased 

under dry conditions (Ristaino and Gumpertz, 2000). 

Exclusion of the A1 mating type from Europe is possible by prohibiting the entry of living plant 

hosts and untreated plant-derived products, compost, and potting media. Based on the general 

biology of heterothallic Phytophthora species, more virulent strains can result from genetic 

recombination (Erwin and Ribeiro, 1996), e.g., P. infestans (Smart and Fry, 2001). Limited 

introductions of European-type isolates of P. ramorum have already occurred in North America 

(Grunwald, 2007) and there is evidence that at least one of these isolates is more aggressive than 

the North American isolates (Garbelotto et al., 2004; Parke et al., 2004a). Exclusion of 

P. ramorum from non-infested areas is possible by prohibiting movement of all hosts (providing 

all hosts have been identified) from infested areas. 

APHIS implemented emergency phytosanitary measures to restrict the movement of nursery 

stock and other plant materials from all European Union member states due to concerns about 

P. ramorum. In addition to the current measures in 7 CFR 319.37, the following apply to 

propagative plant materials of all P. ramorum host plants: 1) the National Plant Protection 

Organization (NPPO), or an agency accredited by the NPPO, must conduct an annual survey of 

nurseries exporting propagative plant materials of host plants to determine that those nurseries 

are free of P. ramorum; 2) the NPPO, or an agency accredited by the NPPO, must inspect all 

shipments of host materials exported to the United States, and must sample and test plants 

bearing symptoms of P. ramorum; and 3) propagative plant materials of host plants must be 

accompanied by a phytosanitary certificate stating that the plants originate in a nursery which is 

inspected and tested annually and found free of P. ramorum and that the plants have been 

inspected prior to export and found free of the pathogen (Aley, 2007). 

47 
 

 

 

Containment 

Under current Federal domestic regulations (7 CFR §301.92), nurseries in the quarantined areas 

must be inspected, sampled, and tested annually for symptoms of P. ramorum. In addition, preshipment inspections are required prior to interstate movement. The Emergency Federal Order 

Restricting Movement of Nursery Stock from California, Oregon, and Washington Nurseries 

(Dec. 21, 2004) and 7 CFR §301.92 also require nurseries in regulated areas of California, 

Oregon, and Washington to have annual and pre-shipment inspections of host materials prior to 

interstate shipment. If the pathogen is detected during any inspection process, eradication efforts 

are initiated. 

Suppression 

Efforts to prevent the spread of P. ramorum from the quarantined counties of California have 

focused on educational outreach, the seasonal closure of trails (COMTF, 2005), and facilities for 

soil removal from shoes (Davidson et al., 2005) and bicycle tires (Tjosvold et al., 2006a). 

In Humboldt County, California, efforts to reduce inoculum load by removing infected trees 

have been initiated (COMTF, 2004c). More recently, a cooperative effort among State and 

Federal agencies and industry has initiated a project to suppress the northward movement of P. 

ramorum by creating a “No Host Zone” (Cannon, 2007). Currently, herbicides are being used to 

kill L. densiflorus in a band seven miles long by two miles wide along the Van Duzen River. 

This band is 20 miles north of the most northern forest detection in California. 

Suppressive mitigation measures used for other Phytophthora species include sanitation, 

disinfectants, fungicides, fumigants, methods of water treatment and distribution, and type and 

form of bed beneath the pots (Erwin and Ribeiro, 1996; Hartmann et al., 2002). Suppression 

efforts for nursery stock and live Christmas trees focused on surveys, the development of best 

management practices, and education of producers (Suslow et al., 2005, 2008) and are currently 

part of the eradication efforts described below. 

Eradication 

Removal and destruction of plant material and related articles are the major eradication efforts 

for P. ramorum in forests and nurseries. When infected plants are found in forests, a buffer area 

of at least 0.25 miles from the outermost infected plants is used to establish the quarantined area 

(APHIS, 2006); in Oregon a buffer area of 0.5 miles is currently used (OSOS, 2007). The only 

current effort to eradicate P. ramorum from a forest setting is underway in Curry County, 

Oregon (Goheen et al., 2002a; Goheen et al., 2007; OSOS, 2007). The recent detection in Curry 

County of P. ramorum in soil six years after host eradication (Kanaskie et al., 2008), coupled 

with research evidence that P. ramorum has a soil phase (Fichtner et al., 2007a, b; Parke et al., 

2004a, 2006b; Shishkoff, 2006; Shishkoff and Tooley, 2004), suggests that additional eradication 

measures may be needed. 

The APHIS-confirmed nursery protocol requires a delimiting survey of the entire nursery, 

including inspection of all host and associated plant (HAP) genera, including plants for sale or 

propagation (APHIS, 2007c). All HAP genera within 2 meters of infected plants will be 

destroyed by incineration, deep burial, or a combination of steam sterilization and deep burial. 

All HAP genera within 10 meters of the positive block(s) shall be considered exposed to 

Phytophthora ramorum and shall be held for the 90-day quarantine period (90 days of conducive 

environmental conditions). In addition to plants, water, media components, and soil will be 

48 
sampled during the delimiting survey. Positive samples will be treated according to the protocol 

(APHIS, 2007c). The USDA has developed a protocol in response to P. ramorum-infected 

plants installed in the landscape (APHIS, 2007e). 

Eradication of the pathogen via chemicals is problematic. The pesticides available for control of 

Phytophthora species (Table 7) are fungistatic and not fungicidal. Additionally, metalaxyl 

resistance has been detected in P. ramorum (Rizzo et al., 2005). Herbicides are being used to kill 

host plants to prevent inoculum survival by the pathogen in forests in Curry County, OR and 

Humboldt County, CA (Goheen et al., 2007; Cannon, 2007). 

Sanitation 

Sanitation in all stages of propagation is necessary to maintain pathogen-free material (Pegg, 

1978 and Hansen, 1970 in Erwin and Ribeiro, 1996; Jones and Benson, 2001). For control of a 

polycyclic foliar pathogen like P. ramorum in the field, sanitation needs to be 99.9% effective 

(Van der Plank, 1963). Sanitation practices should include removal and testing of symptomatic 

nursery stock, sterilization of potting media, and disinfection of tools, benches, workers’ shoes 

and gloves, and other equipment. All symptomatic material or diseased plants should be 

disposed in a sanitary landfill, incinerated, or otherwise treated to prevent the spread of 

P. ramorum. 

Garbelotto et al. (2003) found that 9-12 hours of leaf wetness at 18-22°C are needed to obtain 

significant infections on U. californica leaves. Contaminated irrigation and contaminated 

recycled water disperse Phytophthora propagules, either directly by delivering contaminated 

water or indirectly by splashing inoculum from plant and ground surfaces to other plants (Erwin 

and Ribeiro, 1996; Werres et al., 2007). Methods to disinfest water are available and include 

chlorine products, filters, and ozonation (Hartmann et al., 2002). Water treatment should be 

coupled with testing before and after treatment. The recycling of irrigation water has been 

adopted for environmental reasons, but this process increases the risk of spreading the pathogen. 

Chemical control would include fungicides and disinfectants for benches, tools, and equipment. 

Sodium hypochlorite is a commonly used source of chlorine that is suitable for these surfaces, 

but can be phytotoxic (Hartmann et al., 2002; Jones and Benson, 2001). Pesticides are available 

and registered for use with Phytophthora species (Table 7), but these products are fungistatic and 

not fungicidal. 

49 
Table 7. Fungicides labeled for control of Phytophthora diseases1

. 

ACTIVE INGREDIENT PRODUCT COMPANY REGISTERED 

Azoxystrobin Amistar Syngenta Vegetable crops 

Chlorothalonil Daconil Ultrex Syngenta Ornamentals 

Chlorothalonil Echo 720 T&O SipCam Agro Turf, ornamentals 

Champ Formula 2 flowable, Copper hydroxide Nufarm Ornamentals 

wp 

Copper hydroxide Champion WP Nufarm Ornamentals 

Copper hydroxide Kocide 2000 T/N/O Griffin Turf, ornamentals 

Dimethomorph Acrobat 50WP, MZ BASF Potatoes 

Etridiazole Banrot 40WP, 8G Scotts Ornamentals 

Etridiazole Terrazole 35WP Crompton-Uniroyal Ornamentals 

Etridiazole Truban 25EC, 30WP, 5G Scotts Turf, ornamentals 

Fluaxinam Omega 500F Syngenta Peanuts and potatoes 

Mancozeb Dithane 75 DF Dow Ornamentals 

Mancozeb Fore Dow Turf, ornamentals 

Mancozeb Gavel 75 DF Dow Vegetable crops 

Mancozeb+Cu(OH)2 Mankocide Griffin Fruits and vegetables 

Mefanoxam Apron XL LS Syngenta Vegetable crops 

Mefanoxam Mefanoxam 2 SipCam Agro Ornamentals 

Mefanoxam Ridomil Gold Syngenta Fruits and vegetables 

Phosphonate Aliette WDG Chipco Bayer Turf, ornamentals 

Phosphonate Phostrol Nufarm Fruits and vegetables 

Phosphonate Vital Griffin Ornamentals 

Propamocarb Banol Bayer Turf, ornamentals 

Pyraclostrobin Cabrio EG BASF Fruits and vegetables 

Pyraclostrobin Headline BASF Vegetable crops 

Trifloxystrobin Flint Bayer Fruits and vegetables 1

This list is not comprehensive and does not constitute an endorsement by USDA of any products listed here. 

A series of best management practices based on epidemiological factors could include multiple 

mitigations, such as pathogen-free propagating material, a pathogen-free water source, clean 

potting media, pots, a strict sanitation protocol including cleaning and testing of benches and 

beds, and cleaning of tools, equipment, shoes, hands, etc. The Nursery Committee of the 

California Oak Mortality Task Force (COMTF) began developing best management practices in 

2004, which were modified in 2005 (Suslow et al., 2005). 

The State of Oregon established regulations in 2001 prohibiting the entry of products of 

susceptible oaks from California unless they have been kiln-dried or heat-treated to 71.1°C for 

75 minutes measured at the core (ODA, 2001). Oregon required that soil associated with oak 

commodities be sterilized by dry heat at 110°C for 16 hours (ODA, 2001). After the quarantine 

was enacted in Oregon, the pathogen was detected at several sites in Curry County; all infected 

plants are being burned on site. The eradication efforts in Curry County are cooperative among 

State and Federal agriculture and forestry agencies. 

50 
 

C. Nursery Stock, Christmas Trees, and Cut Foliage/Flowers 

Chemical Treatment 

Linderman et al. (2006b) evaluated fungicides labeled for use on several Phytophthora species 

(P. cactorum, P. citricola, P. nicotiana, P. citrophthora, and P. ramorum). Systemic and 

translaminar fungicides were effective in disease suppression but were not effective as 

eradicants. Of all fungicides tested, menfenoxam was the most effective on all of the species 

tested, with the exception of P. citrophthora. 

Tjosvold et al. (2006a) also evaluated registered products on Rhododendron, Camellia, Pieris, 

and Viburnum. Those products most efficacious on Rhododendron were selected for timing of 

application studies. Maximum rates of mefenoxam (metalaxyl-M), dimethomorf, pyraclostrobin, 

and fenamidone were applied as foliar sprays on wounded and non-wounded leaves. 

Preventative activity was observed for two weeks but not for four weeks. Post-infection 

treatments were ineffective. Only dimethomorf significantly reduced the success of isolation 

recovery from lesions. Metalaxyl –M, azoxystrobin, and fenamidone/mancozeb completely 

inhibited symptom development on Rhododendron spp. (Turner et al., 2006). Heungenis et al. 

(2005) tested the efficacy of metalaxyl, dimethomorf, cyazofanid, fosphetal Al, cymoxanil, and 

mancozeb to control P. ramorum on Rhododendron. Metalaxyl, dimethomorf, and cyazofanid 

were the most effective, fosphetal Al, and cymoxanil were intermediate, and mancozeb was least 

effective. The best control was achieved when the lower leaf surface was covered with the 

fungicide. Fungicides were better as protectants and not effective as curatives (Heungenis et al., 

2005). 

Chastagner et al. (2006a) evaluated 20 systemic and contact fungicides on seedlings of 

Pseudotsuga menziesii var. menziesii. A drench application of mefenoxam prior to bud break 

prevented infection, and post-bud break applications of mancozeb, maneb, and metiram provided 

100% control. Variable results were obtained with other fungicides. The surfactant Latron CS-7, 

applied at post-bud break, yielded 60-100% reduction in infection. A concern associated with the 

potential use of fungicides to control this disease is the possibility that fungicides might suppress 

symptom development on infected plants. Systemic fungicides might have the potential to 

suppress symptom development, but this is not likely with the contact types of fungicides found 

to be effective in protecting seedlings from P. ramorum (Chastagner et al., 2006a). 

Dimethomorph and phosphate were applied to V. ovatum, L. densiflorus, R. macrophyllum, and 

U. californica in the field at one and two times the recommended rates. Detached leaves were 

taken to the laboratory for wound inoculation assays. No treatment provided complete protection 

(Goheen et al., 2006a). 

Biological Control 

Bacillus brevis and Paenibacillus polymixa were tested for antagonistic activity against five 

Phytophthora species, including P. ramorum. Both antagonists significantly inhibited 

P. ramorum in vitro, but were ineffective in inoculation assays of leaves dipped in a cell 

suspension of each Phytophthora species (Linderman and Davis, 2006b). Out of 100 fungi 

bacteria and antinomycetes isolated from soil, leaf surfaces and plant parts, 15 microorganisms 

inhibited P. ramorum in culture; six of these organisms completely inhibited zoospore 

germination while one enhanced germination. Percentage leaf necrosis was less for all six than 

the water control, but none completely inhibited necrosis. (Widmer, 2007). 

51 
Cultural Control 

Sanitation during and after propagation is necessary to maintain and monitor pathogen-free 

material (Pegg, 1978 and Hansen, 1970 in Erwin and Ribeiro, 1996). For control of a polycyclic 

foliar pathogen such as P. ramorum in the field, sanitation needs to be 99.9% effective (Van der 

Plank, 1963 in Erwin and Ribeiro, 1996). Sanitation practices should include removing and 

testing symptomatic stock, sterilizing potting media, and disinfecting tools, benches, and 

workers’ shoes, gloves, and equipment (Erwin and Ribeiro, 1996). All symptomatic material or 

diseased plants should be disposed in a sanitary landfill or otherwise treated to prevent the spread 

of P. ramorum. Micropropagation media have been demonstrated to support the growth of the 

pathogen, facilitating detection (Linderman and Davis, 2007b). 

Irrigation water can be a pathway for dissemination of P. ramorum (Werres et al., 2007), 

especially in water that is re-circulated. A source of pathogen-free water is necessary to prevent 

infection. A variety of methods to disinfest water exist, including ozonation, chlorination, 

filtration, and UV irradiation (Jarvis, 1992; von Broembsen, 2005). Kaminski et al. (2006) built 

and tested three different filtration systems for the non-chemical elimination of P. ramorum. 

Physical Control 

The combined use of heat and vacuum prevented the recovery of P. ramorum from U. 

californica leaves while maintaining the volatiles needed in the leaves for cooking. However, 

the lack of recovery of the pathogen does not necessarily mean that the pathogen has been 

devitalized (Harnik et al., 2004). Linderman and Davis (2005, 2006a, c) demonstrated that 

P. ramorum can readily survive in potting media or soil after deliberate contamination with 

culture-produced sporangia or chlamydospores. They detected the pathogen for six months by 

baiting or direct plating from all contaminated substrates. P. ramorum sporangia survived best in 

peat moss, potting mix, coir, and Douglas fir bark, and poorest in sand or soil. They also found 

that the use of heat via aerated steam mixtures at temperatures of 50oC or higher for 30 minutes 

was an effective means of eradicating P. ramorum from infested media and contaminated 

containers without destroying the containers (Linderman and Davis, 2006a). 

Best Management Practices 

The Nursery Committee of the COMTF has formulated best management practices to control or 

eliminate diseases caused by P. ramorum (Suslow et al., 2005). They divided the practices into 

three categories: exclusion, prevention, and monitoring. 

Suslow (2008) reported that there were three factors responsible for the decline in nursery 

detections: the Federal Order, grower education, and critical nursery research. Pilot programs 

are being initiated to validate selected best management practices (COMTF, 2007; ODA, 2007; 

Suslow, 2008). 

Breeding for Resistance 

Several studies testing host susceptibility suggest resistance to P. ramorum is present in several 

taxa. De Dobbelaere et al. (2006) screened 21 species and 42 hybrids of Rhododendron for 

susceptibility to P. ramorum using four inoculation methods (wounded or non-wounded 

detached leaves and wounded or non-wounded branches). Significant differences in disease 

susceptibility were observed among species as well as among hybrids with all methods used. 

Inoculation of wounded leaves and stems showed that most species and hybrids were susceptible 

to some extent. Inoculation of non-wounded leaves and/or stems resulted in a large degree of 

52 
 

variation in susceptibility. The results suggested that if significant resistance is present, it 

probably occurs at the level of tissue penetration. Shishkoff (2007b) evaluated the relative 

susceptibility of 25 species and cultivars of Syringa to P. ramorum using detached leaf assays. 

The cultivar tested had a significant effect on percent lesion area. Linderman et al. (2006) 

evaluated the effect of different species of Phytophthora and isolates of P. ramorum (both 

mating types) on detached leaves of Rhododendron, Syringa, and Viburnum inoculated under 

controlled conditions. They found significant differences in virulence among Phytophthora 

species and P. ramorum isolates. 

D. Wood and Wood Products 

Woody canker hosts are unique in that sporulation is not observed on the surface of cankers; 

however, the pathogen can be isolated from bark and wood (Davidson et al., 2003b). The 

pathogen was also recovered from firewood stored for six months (Shelly et al., 2005a). 

Sporulation in baiting trials was stimulated when inoculated “logs” were kept at 12°C prior to 

baiting (Garbelotto, 2002). Studies are needed to determine if chlamydospores or dormant 

mycelia are produced in phloem and xylem, and if so, whether these forms of inocula are 

destroyed by natural or kiln drying. 

Physical Treatments 

There are a few treatments available to mitigate this pathogen in wood: physical removal of 

infected bark and wood, air drying, and heat treatment. Phytophthora ramorum has been 

detected in phloem and xylem of multiple tree hosts (Brown and Brasier, 2007; Parke et al., 

2007). Mycelium was found in multiple cells types and chlamydospores were found in the xylem 

vessels of L. densiflorus (Parke et al., 2007). Chlamydospores are considered a survival stage 

for Phytophthora spp. (Erwin and Ribeiro, 1996), but the specific role of this structure in the 

disease cycle of P. ramorum is incompletely known (Fichtner et al., 2007a). 

Debarking is a standard quarantine treatment for the movement of logs and lumber. However, 

Brown and Brasier (2007) have shown that P. ramorum is often active and can remain viable up 

to 25 mm into the xylem, and Parke et al. (2007) have found P. ramorum at depths of 4 cm. 

These data suggest that a more stringent treatment is required to prevent the spread in wood. 

They recommend removal of at least 3 cm of outer sapwood, and where quarantine issues arise it 

may be preferable to destroy the infected trees (Brown and Brasier, 2007). 

Prescribed periods and conditions for air-drying or heat treatment are possible mitigation 

procedures for wood products. In the laboratory, P. ramorum was not recovered from infected 

wood chips after two weeks of drying at 55oC (Swain et al., 2005). It is known that the core 

temperature of piles of bark used for commercial mulch exceeds 55°C (Titko, 2003) indicating a 

potential mitigation. One preliminary study reports that 30 minutes at 56oC, the IPPC standard 

treatment for wood drying, may not be sufficient to devitalize the pathogen (Tubajika et al., 

2008. However, Swain et al. (2005, 2006) found that cultures of P. ramorum were killed after 

exposure to 45oC for 24 hours or 55°C for one hour and that the temperatures in compost piles 

devitalized the pathogen. Microbial competition or other biological activity or products resulting 

from digested plant material may play a role in reducing inoculum (Hoitink and Fahy, 1986). 

Recently, a limited study using a radio frequency treatment on three tree genera indicated some 

success at controlling certain wood decay and sapstaining fungi (Tubajika et al., 2006); however, 

this technique has not been tested against P. ramorum. 

53 
Chemical Control 

P. ramorum is sensitive to copper hydroxide, metalaxyl, phosphate, phosphites, and 

phosphonates (Garbelotto et al., 2002c; Harnik and Garbelotto, 2006; Schmidt et al., 2006). 

Copper hydroxide was effective up to six weeks post-treatment on U. californica (Harnik and 

Garbelotto, 2006). On Quercus spp. and L. densiflorus, phosphite injections and topical 

applications significantly reduced lesion size. However, Kanaskie et al. (2006) found variation in 

application method and effects on lesion size and location on L. densiflorus. A combination of 

injection and topical applications of phosphonate on Q. parvifolia var. shrevei was more 

effective than either treatment alone (Schmidt et al., 2006). All three treatments were more 

effective than the control for L. densiflorus, and dosage may be as important as the application 

method. Range in susceptibility of the hosts to the pathogen may affect the outcome of the 

treatment (Schmidt et al., 2006). 

Methyl bromide has been used as a fumigant for wood products, but the data on control of fungi 

and related organisms in wood are limited. However, methyl bromide has a long history for soil 

fumigation in the field and greenhouse (Erwin and Ribeiro, 1996). It has commonly been used in 

combination with chloropicrin for control of Phytophthora species and other pests in strawberry 

beds (Wilhelm and Paulus, 1980), and has been used as a soil treatment for the mitigation of 

P. cinnamomi in citrus groves (Menge and Nemec, 1997). 

Magnusson et al. (2001) listed methods to mitigate the risk for other pathogens and pests in 

wood chips: heat treatment; pressure impregnation at temperature and pressures to kill fungi, 

insects, and nematodes; and in-transit shipboard fumigation. They also noted that economically 

feasible treatments for wood chips are currently lacking, leaving regulation of trade the sole 

strategy. 

Cultural and Biological Control 

A number of cultural methods are used to mitigate root rot and canker diseases of citrus caused 

by P. cinnamoni and P. citrophthora, including management of the source and the amount of 

nitrogen and water (Menge and Nemec, 1997). Elevated levels of calcium, phosphorus, iron, and 

copper are inhibitory to zoospores of these two species. Most of the measures are to control the 

root rot phase, but the nitrogen and water levels also affect the amount of succulent growth 

produced above ground. Menge and Nemec (1997) recommended cultural measures such as 

pruning low-hanging branches and removal of mulch from the trunk to eliminate moisture on the 

trunk and thereby prevent canker formation. 

Avoiding both overwatering and excess nitrogen application is recommended to reduce the 

likelihood of infection by P. ramorum (Garbelotto, 2003c). Trees with higher water potentials 

are at a higher risk for infection than trees with less than optimal water potentials (Swiecki and 

Bernhardt, 2002a, b). Factors that encourage rapid growth of trees create natural openings and 

thinner cells in the outer bark, and may increase the efficiency of infection by P. ramorum. 

In vitro laboratory research with biological antagonists indicated that control was possible, but 

field tests did not indicate control (Garbelotto, 2003c). 

54 
 

Breeding for Resistance 

Levels of resistance are being detected both in and between populations of U. californica 

(Meshriy et al., 2006) and Quercus (Dodd et al., 2005; Hüberli et al, 2002). Work with a variety 

of hosts and Phytophthora species indicates strategies to use natural resistance. Menge and 

Nemec (1997) found that it was important to consider time of year, cultural factors, and tissue 

that is susceptible when screening for resistance. 

The USDA Forest Service, Pacific Southwest Research Station, the Midpeninsula Open Space 

District, and University of California Berkeley are assessing levels of P. ramorum resistance in 

L. densiflorus. Acorns collected from stands starting at Big Sur into Oregon were used in field 

and laboratory studies to determine the source of and develop a reliable test for resistance 

(Frankel, 2007). 

E. Greenwaste and Compost 

Physical Control 

Evidence exists that composting, as specified by the California Integrated Waste Management 

Board, may be an effective cultural control of P. ramorum in yard waste (Swain and Garbelotto, 

2006; Swain et al., 2005). The minimum temperature required by the State of California for 

pathogen control in compost is 55°C for 3 days (CIWMB, 2007). Swain et al. (2005, 2006) 

found that cultures of P. ramorum were killed after exposure to 55°C for one hour or 45°C for 24 

hours. Tests indicate that P. ramorum in greenwaste mulch is killed in compost after being held 

at 55°C for two weeks (Swain et al., 2006). Phytophthora ramorum could not be recovered by 

baiting from leaf and twig samples after tunnel composting at a minimum of 60°C for 10 hours 

(Aveskamp and Wingelaar, 2006). Similar temperatures can be reached in bark piles; therefore, 

a composting system may be developed (Titko, 2003). Additional information on 

chlamydospore biology, such as factors affecting germination, is needed before composting 

methods can be proven as effective control measures. Heat may not be the only factor 

detrimental to P. ramorum in the composting process. Microbial competition or other biological 

activity or products resulting from digested plant material may play a role in reducing inoculum 

(Hoitink and Fahy, 1986). Composting also requires a monitoring program to ensure that 

P. ramorum is not re-introduced (Garbelotto, 2003a). Research indicates that the source of the 

material may affect the ability of the composting process to devitalize P. ramorum (Swain and 

Garbelotto, 2006). 

F. Potting Media and Soil 

Domestic movement of nursery material allows for movement in plants in potting media; some 

mitigation measures for potting media are covered in section C. 

Physical Control 

Asymptomatic roots and infested potting media can harbor P. ramorum (Fichtner et al., 2007b; 

Linderman and Davis, 2006a, c; Parke et al., 2006b; Shishkoff, 2007). Aerated steam mixtures 

were tested for mitigation potential for P. ramorum and other pathogens in potting media in 

containers. Phytophthora ramorum could not be recovered from media subjected to aerated 

steam mixtures of 60°, 65°, or 75°C for 30 minutes (Linderman and Davis, 2006a). 

A recent study of potential mitigation for P. cinnamomi in soil indicated prescribed burning did 

not attain sufficient temperatures for use as a control (McLaughlin et al., 2007). 

55 
Chemical Control 

Several soil fumigants are listed in APHIS protocols for mitigation in nurseries and landscapes 

with confirmed detections of P. ramorum: chloropicrin, methyl bromide, metam sodium, and 

Dazomet (APHIS 2004c, 2007c). 

Methyl bromide has a long history for soil fumigation in the field and greenhouse (Erwin and 

Ribeiro, 1996). It has commonly been used in combination with chloropicrin for control of 

Phytophthora species and other pests in strawberry beds (Wilhelm and Paulus, 1980), and has 

been used for soil treatment for the mitigation of P. cinnamomi in citrus groves (Menge and 

Nemec, 1997). 

Agrifos® (phosphonate) and Pentrabark® were approved in 2003 by the California Department 

of Pesticide Regulation for use together as a treatment for P. ramorum on Quercus spp. And 

L. densiflorus. The efficacy of this chemical varies with application method and the location of 

the pathogen in plant tissue (Garbelotto et al., 2003; Kanaskie et al., 2006; Schmidt et al., 2006 ). 

Though phosphonate can be applied as a soil drench, Garbelotto et al. (2002c, 2003b) and 

Tjosvold et al. (2006a) found that method ineffective. 

Cultural Control 

Sanitation by removal of plant debris and humus reduced the level of P. ramorum recovered by 

baiting at the soil surface but did not affect recovery at 20 cm (Aveskamp et al., 2006). 

56 
Zoospore release 

Sporulation in or on leaves and twigs 

Sporangia 

Host Infected 

Zoo

an

Direct germination 

Chlamydospores 

Foliar a

hos

Fig. 4. Potential points for the application of mitigation measures for the foliar host phase are indicated with pruning 

57 
Canker host 

phase 

Sporulation at water 

surface from exposed 

inner bark 

Host material harvested 

for wood products: inner 

bark exposed 

Host infected 

Outer bark breeched and 

inner bark infected 

Inoculum splashed 

onto susceptible host 

Fig. 5. Potential points for the application of mitigation measures for the canker host phase are indicated with pruning sh

58 
Spores washed/blown 

to ground Sporulation in or on 

leaves and twigs 

Host Infect

Infected tissue falls to 

ground or on surface of 

potting medium 

Inoculum in 

soil/growing medium 

Susceptible Plant 

Tissue: Roots/Fallen 

Green Leaves 

CP

Fig. 6. Potential points for the application of mitigation measures for the soil phase are indicated with pruning shears. 

59 
Do

p

Sporulation in or on leaves and twigs 

Dormancy Broken 

In Mycelia 

Chlamydospore and Mycelia 

Host 

Dormancy Induced In Chlamydospores or Mycelia 

? 

? 

? 

? 

Dorm

Ch

Dire

Fig. 7. Potential points for the application of mitigation measures for the dormancy phase are indicated with pruning shears. 

60 
VII. Acknowledgements 

Contributors 

Glenn Fowler, Entomologist, USDA-APHIS-PPQ-CPHST-PERAL, Raleigh, NC 

Lynn Garrett, Economist, USDA-APHIS-PPQ-CPHST-PERAL, Raleigh, NC 

Heather Hartzog, Plant Pathologist, USDA-APHIS-PPQ-CPHST-PERAL, Raleigh, NC 

Jonathan Jones, USDA-APHIS-EDP, Riverdale, MD 

Reviewers 

Susan Frankel, USDA-Forest Service, Berkeley, CA 

Lisa M. Ferguson, Plant Pathologist, USDA-APHIS-PPQ-CPHST-PERAL, Raleigh, NC 

Walter Gutierrez, Plant Pathologist, USDA-APHIS-PPQ-CPHST-PERAL, Raleigh, NC 

61 
 

 

VIII. Literature Cited 

Abad, G. 2007. Taxonomic position of Phytophthora species. Personal communication to B. 

Randall-Schadel from Gloria Abad (USDA-APHIS-PPQ-NIS Lead Scientist, Molecular 

Biologist/Plant Pathologist) on October 29, 2007. Archived in PERAL Library, Raleigh, NC. 

Agrios, G. N. 1997. Plant Pathology (4th ed.). Academic Press, San Diego. 

Agrios, G. N. 2005. Plant Pathology (5th ed.). Academic Press, San Diego. 

Aley, W. 2007. Current regulation of P. ramorum—Europe and Canada. Personal 

communication to B. Randall-Schadel from William Aley (USDA-APHIS-PPQ-CIAO Import 

Risk Manager) on October 1, 2007. Archived in PERAL Library, Raleigh, NC. 

Anagnostakis, S. 1987. Chestnut blight the classical problem of an introduced pathogen. 

Mycologia 79:23–37. 

Anon. 2007. Forest Health Highlights in Oregon 2006. Joint Publication of the Oregon 

Department of Forestry and the USDA Forest Service, Pacific Northwest Region, 

R6-NR-FID-TP-02-2007, Portland, Oregon, April 2007. Last accessed November 2, 2007, 

from http://www.oregon.gov/ODF/PRIVATE_FORESTS/docs/fh/2006HighlightsOR.pdf. 

APHIS. 2002. Guidelines for Pathway-Initiated Pest Risk Assessment, Version 5.02. United 

States Department of Agriculture, Animal and Plant Health Inspection Service (APHIS). 

APHIS. 2004a. Confirmed Residential Protocol for Phytophthora ramorum Detections in 

Landscaped Residential or Commercial Settings November 08, 2004. United States 

Department of Agriculture, Animal and Plant Health Inspection Service (APHIS), Plant 

Protection and Quarantine. Archived in PERAL Library, Raleigh, NC. 

APHIS. 2004b. Water Sampling for Phytophthora ramorum in Infested or Potentially 

Infested Nurseries. Adapted from protocols in use by the Oregon Department of Agriculture 

Version 2.1, May 7, 2004. Last accessed November 5, 2007, from 

http://www.aphis.usda.gov/plant_health/plant_pest_info/pram/downloads/pdf_files/watersam 

plingprotocol.pdf. 

APHIS. 2005a. Program Update for Phytophthora ramorum. United States Department of 

Agriculture, Animal and Plant Health Inspection Service (APHIS) Pest Detection and 

Management Programs. January 10, 2005. Last accessed March 23, 2005, from 

http://www.aphis.usda.gov/ppq/ispm/pramorum. 

APHIS. 2005b. Program Update for Phytophthora ramorum. United States Department of 

Agriculture, Animal and Plant Health Inspection Service (APHIS) Pest Detection and 

Management Programs. March 7, 2005. Last accessed March 23, 2005, from 

http://www.aphis.usda.gov/ppq/ispm/pramorum. 

62 
APHIS. 2005c. Phytophthora ramorum (Pr) also known as Sudden Oak Death, ramorum leaf 

blight and ramorum dieback. United States Department of Agriculture, Animal and Plant 

Health Inspection Service (APHIS) Pest Detection and Management Programs. Last accessed 

March 23, 2005, from http://www.aphis.usda.gov/ppq/ispm/pramorum. 

APHIS. 2006. Using ELISA for Phytophthora ramorum Survey. United States Department of 

Agriculture, Animal and Plant Health Inspection Service (APHIS). Last accessed November 

8, 2007, from http://www.aphis.usda.gov/plant_health/plant_pest_info/pram/downloads/ 

pdf_files/ELISA.pdf. 

APHIS. 2007a. APHIS List of Plants Regulated and Associated with Phytophthora ramorum. 

United States Department of Agriculture, Animal and Plant Health Inspection Service 

(APHIS). Revised December 1, 2007. Last accessed December 18, 2007, from 

http://www.aphis.usda.gov/plant_health/plant_pest_info/pram/downloads/pdf_files/usdaprlist 

.pdf. 

APHIS. 2007b. Phytophthora ramorum: quarantine and regulations. Rules and Regulations, 

February 27, 2007. Federal Register 72(38): 8585-8604. 

APHIS. 2007c. Official Regulatory Protocol for Wholesale and Production Nurseries Containing 

Plants Infected with Phytophthora ramorum. Confirmed Nursery Protocol: Version 8.0 

Revised July 20, 2007. United States Department of Agriculture, Animal and Plant Health 

Inspection Service (APHIS), Plant Protection and Quarantine. Last accessed November 5, 

2007, from http://www.aphis.usda.gov/plant_health/plant_pest_info/pram/downloads/ 

pdf_files/CNPv8.0-7-20-07.pdf. 

APHIS. 2007d. Phytophthora ramorum Program update October, 2007. Last accessed January 

11, 2008, from http://www.aphis.usda.gov/plant_health/plant_pest_info/pram/downloads/ 

updates/update-11-7-07.pdf. 

APHIS, 2007e. Official Regulatory Protocol for Phytophthora ramorum Detections in 

Landscaped Residential or Commercial Settings. 08 November 2004 Updated 20 December 

2007. Last accessed January 15, 2008, from http://www.aphis.usda.gov/plant_health/ 

plant_pest_info/pram/downloads/pdf_files/residential_detections_12-07.pdf. 

Aveskamp, M. M., and G. J. Wingelaar. 2006. Elimination of Phytophthora ramorum in the 

tunnel-composting process [abstract]. Page 121 in S. J. Frankel, P. J. Shea, and M. I. Haverty 

(tech. coor.). Proceedings of the Sudden Oak Death Second Science Symposium: The State 

of Our Knowledge. January 18-21, 2005, Monterey, CA. Gen. Tech. Report PSW-GTR-196. 

Albany, CA: Pacific Southwest Research Station, Forest Service, United States Department 

of Agriculture. 

63 
Aveskamp, M. M., P. J. M van Baal, and J. de Gruyter. 2006. Effect of sanitary measures on the 

survival of P. ramorum in soil. Pages 279-284 in S. J. Frankel, P. J. Shea, and M. I. Haverty 

(tech. coor.). Proceedings of the Sudden Oak Death Second Science Symposium: The State 

of Our Knowledge. January 18-21, 2005, Monterey, CA. Gen. Tech. Report PSW-GTR-196. 

Albany, CA: Pacific Southwest Research Station, Forest Service, United States Department 

of Agriculture. 

Bachmann, J. 2002. Woody ornamentals for cut flower growers. Appropriate Technology 

Transfer for Rural Areas. National Center for Appropriate Technology. Last accessed May 2, 

2005, from http://attra.ncat.org/attra-pub/PDF/woodyornamentals.pdf. 

Barrett, T. M. 2006. Pre-epidemic mortality rates for common Phytophthora ramorum host tree 

species in California. Pages 371-378 in S. J. Frankel, P. J. Shea, and M. I. Haverty (tech. 

coor.). Proceedings of the Sudden Oak Death Second Science Symposium: The State of Our 

Knowledge. January 18-21, 2005, Monterey, CA. Gen. Tech. Report PSW-GTR-196. 

Albany, CA: Pacific Southwest Research Station, Forest Service, United States Department 

of Agriculture. 

Barrett, T. M., D. Gatziolis, J. S. Fried, and K. L. Waddell. 2006. Sudden oak death in 

California: What is the potential? Journal of Forestry 104:61-64. 

Beales, P. A., T. Brokenshire, A. V. Barnes, V. C. Barton, and K. J. D. Hughes. 2004a. First 

report of ramorum leaf blight and dieback (Phytophthora ramorum) on Camellia spp. in the 

UK. Plant Pathology 53:524. 

Beales, P. A., A. Schlenzig, and A. J. Inman. 2004b. First report of ramorum bud and leaf blight 

(Phytophthora ramorum) on Syringa vulgaris in the UK. Plant Pathology 53:525. 

Běhalová, M. 2006. Surveys for Phytophthora ramorum in the Czech Republic. EPPO Bulletin 

36(2):393–395. 

Bell, L., and L. Fischer. 2006. 2006 Accomplishment Report Aerial and Targeted Ground-Based 

Monitoring for Sudden Oak Death. USDA Forest Service, State and Private Forestry, Forest 

Health Protection. Last accessed November 2, 2007, from 

http://www.fs.fed.us/r5/spf/fhp/fhm/sod/2006SODAccomplishmentReport.pdf. 

Benson, D. M. 2003. Cultural practices and host resistance: Two IPM strategies for control of 

Phytophthora ramorum in nurseries. Sudden Oak Death Online Symposium 

doi:10.1094/SOD-2003-MB. The American Phytopathological Society. Last accessed 

January 15, 2008, from http://www.apsnet.org/online/proceedings/SOD/pdf/benson.pdf. 

Bilodeau, G. J., C. A. Lévesque, A. W. A. M. de Cock, C. Duchaine, S. Brière, P. Uribe, F. N. 

Martin, and R. C. Hamelin. 2007. Molecular detection of Phytophthora ramorum by realtime polymerase chain reaction using TaqMan, SYBR Green, and molecular beacons. 

Phytopathology 97:632-642. 

64 
 

Blomquist, C., and T. Kubisiak. 2003. Laboratory diagnosis of Phytophthora ramorum from 

field samples. APS Sudden Oak Death Online Symposium, The American Phytopathological 

Society. Last accessed October 5, 2007, from

 http://www.apsnet.org/online/proceedings/sod/Papers/blomquist_kubisiak/default.htm. 

Boutet, X., and A. Chandelier. 2007. Production of viable oospores by Phytophthora ramorum 

[abstract]. Page 52 in Meeting Abstracts of the Fourth International IUFRO Working Party 

7.02.09, Phytophthoras in Forests and Natural Ecosystems. August 26-31, 2007, 

Monterey, California. 

Brasier, C. 2003. Sudden Oak Death: Phytophthora ramorum exhibits transatlantic differences. 

Mycological Research 107:258-259. 

Brasier, C.M. and S. A. Kirk. 2004. Production of gametangia by Phytophthora ramorum in 

vitro. Mycological Research 108:823-827. 

Brasier, C. M., J. Rose, S. A. Kirk, and J. F. Webber. 2002. Pathogenicity of Phytophthora 

ramorum isolates from North America and Europe to bark of European Fagaceae, American 

Quercus rubra, and other forest trees [abstract]. Pages 30-31 in Proceedings of the Sudden 

Oak Death, A Science Symposium, USDA Forest Service and University of California, 

Berkeley. http://danr.ucop.edu/ihrmp/sodsymposium.html. 

Brasier, C., J. Rose, S. Kirk, and J. Webber. 2003. Pathogenicity of Phytophthora ramorum 

isolates from USA and Europe to bark of European forest trees [abstract]. 8th International 

Congress of Plant Pathology, Christchurch, New Zealand (2003-02-02/07). 

Brasier, C., P. Beales, S. Kirk, V. Barton, P. Giltrap, R. Griffin, K. Hughes, C. Lane, J. Rose, 

S. Denham, and J. Webber. 2004a. A new Phytophthora species affecting European Beech 

(Fagus sylvatica) and Rhododendron in the UK. Poster presented at Phytophthora ramorum: 

A Review of North American and European Activity: California Oak Mortality Task Force 

Annual Meeting. March 10, 2004. 

Brasier, C. M., S. Denman, A. Brown, and J. A. Webber. 2004b. Sudden oak death 

(Phytophthora ramorum) discovered on trees in Europe. Mycological Research 

108(10):1107-1110. 

Brasier, C. M., S. Denman, J. Rose, S. A. Kirk, K. J. D. Hughes, R. L. Griffin, C. R. Lane, A. J. 

Inman, and J. F. Webber. 2004c. First report of ramorum bleeding canker on Quercus falcata 

caused by Phytophthora ramorum. Plant Pathology 53:804. 

Brasier, C. M., P. A. Beales, S. A. Kirk, S. Denman, and J. Rose. 2005. Phytophthora kernoviae 

sp. nov., an invasive pathogen causing bleeding stem lesions on forest trees and foliar 

necrosis of ornamentals in the UK. Mycological Research. 109(8):853-859. 

65 
 

Brasier, C., T. Jung, and W. Osswald (eds.). 2006a. Progress in Research on Phytophthora 

Diseases of Forest Trees. Proceedings of the Third International IUFRO Working Party 

07.02.09. September 11-18, 2004, Freising, Germany. Forest Research, Farnham, UK. 

Brasier, C. M., S. A. Kirk, and J. Rose. 2006b. Adaptive differences between Phytophthora 

ramorum isolates from Europe and North America: evidence for separate subspecies? 

[abstract] p 121 in S. J. Frankel, P. J. Shea, and M. I. Haverty (tech. coor.). Proceedings of 

the Sudden Oak Death Second Science Symposium: The State of Our Knowledge. January 

18-21, 2005, Monterey, CA. Gen. Tech. Report PSW-GTR-196. Albany, CA: Pacific 

Southwest Research Station, Forest Service, United States Department of Agriculture. 

Brasier, C., A. Brown, J. Rose, and S. Kirk. 2007. Infection of Tree Stems by Zoospores of 

Phytophthora ramorum and P. kernoviae. [abstract]. in Sudden Oak Death Science 

Symposium III. March 5-9, 2007, Santa Rosa, California. Last accessed October 31, 2007, 

from http://nature.berkeley.edu/comtf/sodsymposium/PDF/Abstracts/ 

Infection%20of%20Tree%20Stems%20by%20Zoospores-Brasier.pdf 

Brown, A. and C. M. Brasier. 2007. Colonization of tree xylem by Phytophthora ramorum, 

P. kernoviae and other Phytophthora species. Plant Pathology DOI: 10.1111/j.1365-

3059.2006.01511.x. 

Bulluck, R., P. Shiel, P. Berger, D. Kaplan, G. Parra, W. Li, L. Levy, J. Keller, M. Reddy, N. 

Sharma, M. Dennis, J. Stack, J. Pierzynski, J. O'Mara, C. Webb, L. Finley, K. Lamour, J. 

McKemy, and M. Palm. 2006. A comparative analysis of detection techniques used in US 

regulatory programs to determine presence of Phytophthora ramorum in Camellia japonica 

'Nucio's Gem' in an infested nursery in Southern California. Plant Health Progress. 

http://www.plantmanagementnetwork.org/php/default.asp. 

Cannon, P. 2007. DRAFT Quarterly Report: Sudden Oak Death Host Reduction Zone. 

Personal communication to B. Randall-Schadel from P. Cannon (USDA Forest Service), 

November 7, 2007. Archived in the PERAL Library, Raleigh, NC. 

Cave, G. L., B. L. Randall-Schadel, and S. C. Redlin. 2005. Risk analysis for Phytophthora 

ramorum Werres, de Cock & Man in’t Veld, causal agent of phytophthora canker (sudden 

oak death), ramorum leaf blight, and ramorum dieback. May 05, 2005. USDA, APHIS, PPQ, 

Center for Plant Health Science and Technology, Plant Epidemiology and Risk Analysis 

Laboratory. Raleigh, NC. 

Chastagner, G. A., E. M. Hansen, K. L. Riley and W. Sutton. 2004. Susceptibility of conifer 

shoots to infection by Phytophthora ramorum. Phytopathology 94:S16. 

66 
Chastagner, G. A., E. M. Hansen, K. L. Riley, and W. Sutton. 2006a. Effectiveness of fungicides 

in protecting Douglas-fir shoots from infection by Phytophthora ramorum [abstract]. Page 

239 in S. J. Frankel, P. J. Shea, and M. I. Haverty (tech. coor.). Proceedings of the Sudden 

Oak Death Second Science Symposium: The State of Our Knowledge. January 18-21, 2005, 

Monterey, CA. Gen. Tech. Report PSW-GTR-196. Albany, CA: Pacific Southwest Research 

Station, Forest Service, United States Department of Agriculture. 

Chastagner, G. A., E. M. Hansen, K. L. Riley and W. Sutton. 2006b. Susceptibility of conifer 

shoots to infection by Phytophthora ramorum. [abstract]. Page 77 in S. J. Frankel, P. J. Shea, 

and M. I. Haverty (tech. coor.). Proceedings of the Sudden Oak Death Second Science 

Symposium: The State of Our Knowledge. January 18-21, 2005, Monterey, CA. Gen. Tech. 

Report PSW-GTR-196. Albany, CA: Pacific Southwest Research Station, Forest Service, 

U.S. Department of Agriculture. 

Chastagner, G. A., K. Riley, and N. Dart. 2008 (in press). Recovery of Phytophthora ramorum 

from mistletoe and California bay inflorescences and possible implications relating to disease 

spread. Proceedings of the Sudden Oak Death Symposium III. March 5-9, 2007, Santa Rosa, 

California. 

CIWMB. 2007. Chapter 3.1. Composting Operations Regulatory Requirements. Regulations: 

Title 14, Natural Resources--Division 7. California Integrated Waste Management Board. 

COMTF. 2003. January Monthly Report, California Oak Mortality Task Force. Last accessed 

February 20, 2004, from http://www.cnr.berkeley.edu/comtf. 

COMTF. 2004a. Sanitation and reducing the spread. California Oak Mortality Task Force, 

September 2004. Last accessed October 5, 2007, from http://www.suddenoakdeath.org/. 

COMTF. 2004b. December Monthly Report, California Oak Mortality Task Force. Last accessed 

March 16, 2004, from http://www.cnr.berkeley.edu/comtf/. 

COMTF. 2004c. March Monthly Report, California Oak Mortality Task Force. Last accessed 

March 16, 2004, from http://www.cnr.berkeley.edu/comtf/. 

COMTF. 2005. Nursery Chronology. California Oak Mortality Task Force. Last accessed May 4, 

2005, from http://nature.berkeley.edu/comtf/html/chronology.htm. 

COMTF. 2007. California Oak Mortality Task Force Report June 2007. Last accessed October 

31, 2007, from 

http://nature.berkeley.edu/comtf/pdf/Monthly%20Reports/COMTF_Report_June_2007.pdf. 

Condeso, T. E. and R. K. Meentemeyer. 2007. Effects of landscape heterogeneity on the 

emerging forest disease sudden oak death. Journal of Ecology 95: 364-375. 

67 
Cree, L., E. Allen, and D. McKenney. 2001. Sudden Oak Death Phytophthora ramorum: Plant 

Health Risk Assessment PRA # 00-39 Draft. October 2001. Canadian Food Inspection 

Agency. 

Cree, L. 2002. Phytophthora ramorum, Sudden Oak Death. Pest Fact Sheet. February, 2002. 

Canadian Food Inspection Agency. 

Cushman, J. H., and R. K. Meentemeyer. 2006. The role of humans in the dispersal and spread of 

Phytophthora ramorum [abstract]. Pages 161-163 in S. J. Frankel, P. J. Shea, and M. I. 

Haverty (tech. coor.). Proceedings of the Sudden Oak Death Second Science Symposium: 

The State of Our Knowledge. January 18-21, 2005, Monterey, CA. Gen. Tech. Report PSWGTR-196. Albany, CA: Pacific Southwest Research Station, Forest Service, United States 

Department of Agriculture. 

Dart, N. L., and G. A. Chastagner. 2007. Estimated economic losses associated with the 

destruction of plants due to Phytophthora ramorum quarantine efforts in Washington State. 

Plant Management Network. Plant Health Progress doi:10.1094/PHP-2007-0508-02-RS. Last 

accessed August 27, 2007, from 

http://www.plantmanagementnetwork.org/sub/php/research/2007/quarantine/. 

Davidson, J. M., M. Garbelotto, S. T. Koike, and D. M. Rizzo. 2002a. First Report of 

Phytophthora ramorum on Douglas-Fir in California. Plant Disease 86:1274. 

Davidson, J. M., P. E. Maloney, A. C. Wickland, A. C. Morse, C. E. Jensen, and D. M. Rizzo. 

2002b. Transmission of Phytophthora ramorum via Umbellularia californica (California 

bay) leaves in California oak woodlands [abstract]. Page 9 in Proceedings of the Sudden Oak 

Death, A Science Symposium, USDA Forest Service and University of California, Berkeley. 

Davidson, J. M., D. M. Rizzo, M. Garbelotto, S. A. Tjosvold, and G. W. Slaughter. 2002c. 

Phytophthora ramorum and sudden oak death in California: II. Transmission and survival. 

Pages 741-749 in R. Standiford and D. McCreary (eds.) 5th Symposium on California Oak 

Woodlands. United States Department of Agriculture For. Serv. Gen. Tech. Rep. PSWGTR-184. 

Davidson, J. M., D. M. Rizzo, M. Garbelotto, S. Tjosvold, G. W. Slaughter, and C. Wickland. 

2003a. Evidence for aerial transmission of Phytophthora ramorum among Quercus and 

Lithocarpus in California woodlands. Page 108-114 in J. A. McComb, G. E. St. J. Hardy and 

I. C. Tommerup (eds.) 'Phytophthora in Forests and Natural Ecosystems'. 2nd International 

IUFRO Meeting on Phytophthora in Forests and Natural Ecosystems, Albany, Western 

Australia. Murdoch University Print, Perth, Australia. 

Davidson, J. M., S. Werres, M. Garbelotto, E. M. Hansen, and D. M. Rizzo. 2003b. Sudden Oak 

Death and Associated Diseases Caused by Phytophthora ramorum. Plant Health Progress 

2003-0707-01-DG. Last accessed May 3, 2005, from 

http://www.plantmanagementnetwork.org/pub/php/diagnosticguide/2003/sod. 

68 
Davidson, J. M., A. C. Wickland, H. A. Patterson, K. R. Falk, and D. M. Rizzo. 2005. 

Transmission of Phytophthora ramorum in mixed-evergreen forest in California. 

Phytopathology 95:587-596. 

de Cock, A. W. A. M., and C. A. Lévesque. 2004. New species of Pythium and Phytophthora. 

Studies in Mycology 50:481–487. 

De Debobboleare, I., K. Heungens, and M. Maes. 2006. Susceptibility Levels of Rhododendron 

Species and Hybrids to Phytophthora ramorum. Pages 79-81 in S. J. Frankel, P. J. Shea, and M. 

I. Haverty (tech. coor.). Proceedings of the Sudden Oak Death Second Science Symposium: 

The State of Our Knowledge. January 18-21, 2005, Monterey, CA. Gen. Tech. Report PSWGTR-196. Albany, CA: Pacific Southwest Research Station, Forest Service, United States 

Department of Agriculture. 

DEFRA. 2004a. Background – Phytophthora ramorum. Department for Environment, Food and 

Rural Affairs, United Kingdom. Last accessed February 20, 2004, from 

http://www.defra.gov.uk/planth/oak.htm. 

DEFRA. 2004c. Phytophthora ramorum epidemiology: sporulation potential, dispersal, 

infection, latency and survival. Final Project Report PH0194, Department for Environment, 

Food and Rural Affairs (DEFRA), United Kingdom. Last accessed December 15, 2004, 

from http://www.defra.gov.uk/science/project_data/DocumentLibrary/PH0194/ 

PH0194_2004_FRP.pdf. 

DEFRA. 2004d. Eradication and containment action required against findings of Phytophthora 

ramorum and Phytophthora kernoviae. Department for Environment, Food and Rural 

Affairs, United Kingdom. Last accessed March 15, 2005, from 

http://www.defra.gov.uk/planth/newsitems/eradcon.htm. 

DEFRA. 2005a. Phytophthora kernoviae – Frequently Asked Questions. The Forestry 

Commission, Department of the Environment, Forest and Rural Affairs (DEFRA), United 

Kingdom. Last accessed February 25, 2005, from http://www.forestry.gov.uk/forestry/infd5vtlel. 

DEFRA. 2005b. Phytophthora ramorum Industry Liaison Group, Fourth Meeting 22 February 

2005. Department of the Environment, Forest and Rural Affairs (DEFRA), United Kingdom. 

Last accessed March 22, 2005, from 

http://www.defra.gov.uk/planth/newsitems/industry.htm. 

DEFRA. 2006. Phytophthora ramorum - a threat to our trees, woodland and healthland. DEFRA 

publication PB12177. Department for Environment, Food and Rural Affairs, United 

Kingdom. Last accessed October 30, 2007, from 

http://www.defra.gov.uk/planth/pestnote/newram.pdf. 

69 
Denman, S., E. Moralejo, S. A. Kirk, E. Orton, and A. Whybrow. 2008 (in press). Sporulation of 

Phytophthora ramorum and P. kernoviae on asymptomatic foliage and fruit. Proceedings of 

the Sudden Oak Death Symposium III. March 5-9, 2007, Santa Rosa, California. 

Dick, M. W. 2001. Straminipilous Fungi: Systematics of the Peronosporomycetes including 

accounts of the marine straminipilous protists, the plasmodiophorids and similar organisms. 

Kluwer Academic Publishers, Dordrecht. 

Dick, M. W., P. T. W. Wong, and G. Clark. 1984. The identity of the oomycete causing ‘Kikyu 

yellows’ with a reclassification of the downy mildews. Botanical Journal of the Linnean 

Society 89:171-197. 

Dodd, R. S., D. Huberli, V. Douhovnikoff, R. Harnik, Z. Afzal-Rafii, and M. Garbelotto. 2002. 

Towards a Model of the Genetic Architecture of Phytophthora ramorum Susceptibility in 

Coast Live Oak [abstract]. Page 35 in: Proceedings of the Sudden Oak Death, A Science 

Symposium, USDA Forest Service and University of California, Berkeley. 

Dodd, R., D. Hüberli, V. Douhovnikoff, R. Y. Harnik, A. Afzal-Rafii, and M. Garbelotto. 2005. 

Is variation in susceptibility to Phytophthora ramorum correlated with population genetic 

structure in coast live oak (Quercus agrifolia Née)? New Phytologist 165:203-214. 

Donahoo, R., C. L. Blomquist, S. L. Thomas, J. K. Moulton, D. E. L. Cooke, and K. H. Lamour. 

2006. Phytophthora foliorum sp nov., a new species causing leaf blight of azalea. 

Mycological Research 110:1309-1322. 

EPPO (European Plant Protection Organization). 2004. Phytophthora ramorum Sudden Oak 

Death. European Plant Protection Organization Panel Review: 2004-03. Last accessed 

January, 2004, from http://www.eppo.org/QUARANTINE/Alert_List/fungi/oak_death.htm. 

Erwin, D. C., and O. K. Ribeiro. 1996. Phytophthora diseases worldwide. APS Press, The 

American Phytopathological Society, St. Paul, MN. 

EC. 2007. Commission Decision 2007/201/EC of 27 March 2007 amending Decision 

2002/757/EC on provisional emergency phytosanitary measures to prevent the introduction 

into and the spread within the Community of Phytophthora ramorum Werres, De Cock & 

Man in‘t Veld sp. nov. European Commission. Official Journal of the European Union, L 90, 

50(90):83-85. 

EXCERPT. 2007. Product Requirements for Australia, Canada, the European Union, Korea and 

Switzerland. Export Certification Project, Perdue Research Foundation, Perdue University, 

Indiana. Last accessed October 16, 2007, from http://excerpt.ceris.purdue.edu/. 

70 
Fichtner, E. J., S. C. Lynch, and D. M. Rizzo. 2004. Survival of Phytophthora ramorum in 

infected leaf tissue at the soil surface in a tanoak-redwood forest [abstract]. Conference of 

Phytophthoras in Forest and Natural Ecosystems. International Union of Forest Research 

Organizations. Last accessed January 13, 2005, from http://www.lwf.uni-muenchen.de/iufroonline/index.html. 

Fichtner, E. J., S. C. Lynch, and D. M. Rizzo. 2006a. Detection and distribution of Phytophthora 

ramorum in soils [abstract], p. 501 in S. J. Frankel, P. J. Shea, and M. I. Haverty (tech. 

coor.). Proceedings of the Sudden Oak Death Second Science Symposium: The State of Our 

Knowledge. January 18-21, 2005, Monterey, CA. Gen. Tech. Report PSW-GTR-196. 

Albany, CA: Pacific Southwest Research Station, Forest Service, United States Department 

of Agriculture. 

Fichtner, E. J., S. C. Lynch, and D. M. Rizzo. 2006b. Summer survival in Phytophthora 

ramorum in forest soils [abstract]. Pages 165-166 in S. J. Frankel, P. J. Shea, and M. I. 

Haverty (tech. coor.). Proceedings of the Sudden Oak Death Second Science Symposium: 

The State of Our Knowledge. January 18-21, 2005, Monterey, CA. Gen. Tech. Report PSWGTR-196. Albany, CA: Pacific Southwest Research Station, Forest Service, United States 

Department of Agriculture. 

Fichtner, E. J., S. C. Lynch, and D. M. Rizzo. 2007a. Detection, distribution, sporulation, and 

survival of Phytophthora ramorum in a California redwood-tanoak forest soil. 

Phytopathology 97:1366-1375. 

Fichtner, E. J., D. M. Rizzo, S. A. Kirk, A. Whybrow, and J. Webber. 2007b. Root associations 

of Phytophthora ramorum and Phytophthora kernoviae in UK woodlands [abstract]. Pages 

54-55 in 4th IUFRO Phytophthoras in Forests & Natural Ecosystems, Meeting Abstracts, 

August 26-31, 2007. 

Frankel, S. 2007. P. ramorum monitoring in CA – description. Personal communication to B. 

Randall-Schadel from S. Frankel (USDA Forest Service) on October 29, 2007. Archived in 

the PERAL Library, Raleigh, NC. 

Garbelotto, M. 2002. Sporangial production on mini logs after storage at 12oC. Personal 

communication to B. Randall-Schadel and others attending a IUFRO research update session 

from M. Garbelotto (Forest Pathologist, University of California at Berkeley), December 16, 

2002. Archived in the PERAL Library, Raleigh, NC. 

Garbelotto, M. 2003a. Providing a solution composting as a control for sudden oak death disease. 

Biocycle 44:53-56. 

Garbelotto, M. 2003b. A report on a comprehensive series of experiments, both in vitro and in 

planta, to develop treatments for Phytophthora ramorum, the cause of Sudden Oak Death. 

http://www.cnr.berkeley.edu/garbelotto/downloads/DPR_rep.pdf. 

71 
Garbelotto, M. 2003c. Treatments [oral presentation]. An arboricultural look at sudden oak 

death. California Oak Mortality Task Force, Spring Meeting, May 28, 2003. Notes by B. 

Randall-Schadel archived in the PERAL Library, Raleigh, NC. 

Garbelotto, M., D. M. Rizzo, and J. M. Davidson. 2001. Studies in the genetics of a new 

Phytophthora species associated with Sudden Oak Death in California. Phytopathology 

91:S110. 

Garbelotto, M., D. M. Rizzo, J. M. Davidson, and S. J. Frankel. 2002a. How to recognize the 

symptoms of the diseases caused by Phytophthora ramorum, causal agent of Sudden Oak 

Death. USDA Forest Service, Pacific Southwest Region publication, pp. 1-15. 

Garbelotto, M., D. M. Rizzo, K. Hayden, M. Meija-Chang, J. M. Davidson, and S. Tjosvold. 

2002b. Phytophthora ramorum and sudden oak death in California. III. Pathogen genetics in 

R. Standiford and D. McCreary (eds.) 5th Symposium on California Oak Woodlands. USDA 

Forest Service, Gen Tech PSW-GTR-184:765-774. 

Garbelotto, M., D. M. Rizzo, and L. Marais. 2002c. Phytophthora ramorum and Sudden Oak 

Death in California: IV. Chemical control, in R. Standiford and D. McCreary (eds.). 5th 

Symposium on California Oak Woodlands. USDA Forest Service, General Technical Report, 

PSW-GTR-184:811-818. 

Garbelotto, M, J. M. Davidson, K. Ivors, P. E. Maloney, D. Huberli, S. T. Koike, and D. M. 

Rizzo. 2003. Non-oak native plants are main hosts for sudden oak death pathogen in 

California. California Agriculture 57(1):18-23. 

Garbelotto, M., K. Ivors, and P. Bonants. 2004. Microsatellite analysis reveals genetic variation 

in Phytophthora ramorum, mitotic recombination, and sexual recombination between A1 

And A2 [abstract]. Conference of Phytophthoras in Forest and Natural Ecosystems, 

September 11-17, 2004. International Union of Forest Research Organizations. Last accessed 

January 13, 2005, from http://www.lwf.uni-muenchen.de/iufro-online/index.html. 

Goheen, E.M., E. M. Hansen, A. Kanaskie, M. G. McWilliams, N. Osterbauer, and W. Sutton. 

2002a. Sudden oak death caused by Phytophthora ramorum in Oregon. Plant Disease 86:441. 

Goheen, E.M., E. M. Hansen, A. Kanaskie, M. G. McWilliams, N. Osterbauer, and W. Sutton. 

2002b. Eradication of sudden oak death in Oregon. Phytopathology 92:S30. Publication 

number P-2002-0213-AMA. 

Goheen, E., E. Hansen, W. Sutton, A. Kanaskie, M. McWilliams, and N. Ostebauer. 2002c. 

Epidemiology of Phytophthora ramorum in Oregon forests [abstract]. Page 10 in 

Proceedings of the Sudden Oak Death, A Science Symposium, USDA Forest Service and 

University of California – Berkeley. 

72 
Goheen, E., M. McWilliams, A. Kanaskie, N. Osterbauer, E. Hansen, and W. Sutton. 2002d. 

Sudden oak death surveys in Oregon—2001 and 2002 [abstract]. Page 23 in Proceedings of 

the Sudden Oak Death, A Science Symposium, USDA Forest Service and University of 

California, Berkeley. 

Goheen, E. M., A. Kanaskie, J. Parke, M. Roth, N. Osterbauer, and A. Trippe. 2006a. 

Applications of fungicides to protect four hosts from foliar infection by Phytophthora 

ramorum in Curry County, Oregon. Pages 513-514 in S. J. Frankel, P. J. Shea, and M. I. 

Haverty (tech. coor.). Proceedings of the Sudden Oak Death Second Science Symposium: 

The State of Our Knowledge. January 18-21, 2005, Monterey, CA. Gen. Tech. Report PSWGTR-196. Albany, CA: Pacific Southwest Research Station, Forest Service, United States 

Department of Agriculture. 

Goheen, E. M., E. Hansen, A. Kanaskie, N. Osterbauer, J. Parke, J. Pscheidt, and G. Chastagner. 

2006b. Sudden oak death and Phytophthora ramorum. A guide for forest managers, 

Christmas tree growers, and forest-tree nursery operators in Oregon and Washington. Oregon 

State University Extension Bulletin EM 8877. Last accessed October 30, 2007, from 

http://extension.oregonstate.edu/catalog/pdf/em/em8877.pdf. 

Goheen, E. M., E. M. Hansen, and A. Kanaskie. 2007. Persistence of Phytophthora ramorum 

after eradication treatments in Oregon tanoak forests. Page 36 in Meeting Abstracts of the 

Fourth International IUFRO Working Party 7.02.09, Phytophthoras in Forests and Natural 

Ecosystems. August 26-31, 2007, Monterey, California. 

Grunwald, N. 2007. Phytophthora ramorum Multilocus Genotyping Database. Last accessed 

November 7, 2007, from http://oregonstate.edu/%7Egrunwaln/phytophthora.php. 

Hall, J. P. and B. Moody. 1994. Forest Depletions Caused by Insects and Diseases in Canada 

1982-1987. Forest Insect and Disease Survey Information Report ST-X-8, Ottawa, Canada: 

Forest Insect and Disease Survey, Canadian Forest Service, Natural Resources Canada. 

Hansen, E. M., and W. Sutton. 2006. Persistence of Phytophthora ramorum after eradication 

efforts in Oregon Tanoak Forests. [abstract], Page 517 in S. J. Frankel, P. J. Shea, and M. I. 

Haverty (tech. coor.). Proceedings of the Sudden Oak Death Second Science Symposium: 

The State of Our Knowledge. January 18-21, 2005, Monterey, CA. Gen. Tech. Report PSWGTR-196. Albany, CA: Pacific Southwest Research Station, Forest Service, United States 

Department of Agriculture. 

Hansen, E. M., D. J. Goheen, E. S. Jules, and B. Ullian. 2000. Managing Port-Orford cedar and 

the introduced pathogen Phytophthora lateralis. Plant Disease 84:4–13. 

Hansen, E., W. Sutton, J. Parke, and R. Linderman. 2002. Phytophthora ramorum and Oregon 

forest trees—one pathogen, three diseases [abstract], pp. 78-79 in Proceedings of the Sudden 

Oak Death, A Science Symposium, USDA Forest Service and University of California, 

Berkeley. 

73 
Hansen, E. M., P. W. Reeser, W. Sutton, and L. M. Winton. 2003a. First report of A1 mating 

type of Phytophthora ramorum in North America. Plant Disease 87:1267 

Hansen, E. M., P. Reeser, J. M. Davidson, M. Garbelotto, K. Iverson, L. Douhan, and D. M. 

Rizzo. 2003b. Phytophthora nemorosa, a new species causing cankers and leaf blight of 

forest trees in California and Oregon, U.S.A. Mycotaxon 88:129-138. 

Hansen, E. M., J. L. Parke, and W. Sutton. 2005. Susceptibility of Oregon forest trees and shrubs 

to Phytophthora ramorum: A comparison of artificial inoculation and natural infection. Plant 

Disease 89:63-70. 

Hardy, G. E., S. Barrett, and B. L. Shearer. 2001. The future of phosphite as a fungicide to 

control the soilborne plant pathogen Phytophthora cinnamomi in natural ecosystems. Austria 

Plant Pathology 30:133–39 

Harnik, T. Y., M. Mejia-Chang, J. Lewis, and M. Garbelotto. 2004. Efficacy of heat-based 

treatments in eliminating the recovery of the sudden oak death pathogen (Phytophthora 

ramorum) from infected California bay laurel leaves. HortScience 39(7):1677-1680. 

Harnik, T. Y., and M. Garbelotto. 2006. Effect of chemicals on hyphal growth, sporangia 

production and zoospore germination of Phytophthora ramorum. [abstract]. Page 517 in S. J. 

Frankel, P. J. Shea, and M. I. Haverty (tech. coor.). Proceedings of the Sudden Oak Death 

Second Science Symposium: The State of Our Knowledge. January 18-21, 2005, Monterey, 

CA. Gen. Tech. Report PSW-GTR-196. Albany, CA: Pacific Southwest Research Station, 

Forest Service, United States Department of Agriculture. 

Hartmann, H. T., D. E. Kester, F. T. Davies, Jr., and R. L. Geneve (7th ed.). 2002. Hartmann and 

Kester’s Plant Propagation Principles and Practices. Prentice Hall, New Jersey. 

Hayden, K. J., D. Rizzo., J. Tse, and M. Garbelotto. 2004. Detection and quantification of 

Phytophthora ramorum from California forests using a real-time polymerase chain reaction 

assay. Phytopathology 94:1075-1083. 

Heungenis, K., I. De Dobbelaere, and M. Maes. 2005. Fungicide control of Phytophthora 

ramorum on Rhododendron. [abstract], p. 46 in Sudden Oak Death Second Science 

Symposium The State of our Knowledge. January 18-21, 2005, Monterey, California. 

Hoitink, H. A. J., and P. C Fahy. 1986. Basis for the control of soilborne plant pathogens with 

compost. Annual Review of Phytopathology 24:93-114. 

Hüberli, D., W. van Sant, S. Swain, J. Davidson, and M. Garbelotto. 2002. Resistance of 

Umbellularia californica (Bay Laurel) to Phytophthora ramorum [abstract], p. 36 in 

Proceedings of the Sudden Oak Death, A Science Symposium, USDA Forest Service and 

University of California, Berkeley. 

74 
Hughes, K. J. D., J. A. Tomlinson, R. L. Griffin, N. Boonham, A. J. Inman, and C. R. Lane. 

2006. Development of a one-step real-time polymerase chain reaction assay for diagnosis of 

Phytophthora ramorum. Phytopathology 96:975-981. 

IPPC. 2002. Glossary of Phytosanitary Terms, ISPM No. 5. International Plant Protection 

Convention (IPPC), FAO, Rome. 

Ivors, K., M. Garbelotto, I. D. E. Vries, C. Ruyter-Spira, B. T. E. Heckkert, N. Rosenzweig, and 

P. Bonants. 2006. Microsatellite markers identify three lineages of Phytophthora ramorum in 

US nurseries, yet single lineages in US forest and European nursery populations. Molecular 

Ecology 15:1493–1505. 

Ivors, K. L., K. J. Hayden, P. J. M. Bonants, D. M. Rizzo, and M. Garbelotto. 2004. AFLP and 

phylogenetic analyses of North American and European populations of Phytophthora 

ramorum. Mycological Research 108(4):378–392. 

Jarvis, W. R. 1992. Managing Diseases in Greenhouse Crops. APS Press, The American 

Phytopathology Society, St. Paul, MN. 

Jerado, A. 2004. Floriculture and Nursery Crops Situation and Outlook Yearbook. United States 

Department of Agriculture. Economic Research Service FLO-2004. June, 2004. 

Jerado, A. 2007. Floricultural and Nursery Crop, Situation and Outlook Yearbook. USDA, 

Economic Research Service. FLO-2007. 

Jones, D. R. 2002. Revised pest risk assessment of the Phytophthora ramorum. CSL (Central 

Science Laboratory), York, UK: 11 January 2002: PPP 9602. 

Jones, D. R., S. Sansford, and C. Brasier. 2003. Sudden Oak Death. Summary Pest Risk 

Analysis. Revision Number: 3. Date: 20 March 2003. Central Science Laboratory, UK 

Department of Environment, Food and Rural Affairs and Forest Research, UK Forestry 

Commission, Last accessed May 5, 2004, from http://www.defra.gov.uk/planth/pra/sudd.pdf. 

Jones, R. K., and D. M. Benson (eds.). 2001. Diseases of woody ornamentals and trees in 

nurseries. APS Press, American Phytopathological Society, St. Paul, MN. 482 pp. 

Jordan, S. 2003. Questionnaire for Santa Cruz and Santa Clara Counties re. nursery potting 

material and Correction. Personal communications to B. Randall-Schadel from S. Jordan 

(PPQ) on March 11 and March 20, 2007. Archived in the PERAL Library, Raleigh, NC. 

Kahn, R. P. 1991. Exclusion as a plant disease control strategy. Annual Review of 

Phytopathology 29:219-246. 

75 
Kaminski, K., T. Ufer, H. Beltz, R. Lüttmann, M Posner, H. P. Wessels, and T. Brand. 2006. 

Introduction of filtration systems in container nurseries for non-chemical elimination of 

Phytophthora spp. from irrigation water [abstract]. Pages 287-289 in S. J. Frankel, P. J. Shea, 

and M. I. Haverty (tech. coor.). Proceedings of the Sudden Oak Death Second Science 

Symposium: The State of Our Knowledge. January 18-21, 2005, Monterey, CA. Gen. Tech. 

Report PSW-GTR-196. Albany, CA: Pacific Southwest Research Station, Forest Service, 

United States Department of Agriculture. 

Kanaskie, A., E. Hansen, W. Sutton, and E. Goheen. 2006. Effects of phosphonate treatments on 

the growth of Phytophthora ramorum in tanoak stems. Pages 259-261 in S. J, Frankel, P. J. 

Shea, and M. I. Haverty (tech. coor.). Proceedings of the Sudden Oak Death Second Science 

Symposium: The State of Our Knowledge. January 18-21, 2005, Monterey, CA. Gen. Tech. 

Report PSW-GTR-196. Albany, CA: Pacific Southwest Research Station, Forest Service, 

United States Department of Agriculture. 

Kanaskie, A., M. McWilliams, E. Goheen, E. Hansen, W. Sutton, and P. Reeser. 2008 (in press). 

Eradication of Phytophthora ramorum from Oregon forests: Status after six years. 

Proceedings of the Sudden Oak Death Symposium III. March 5-9, 2007, Santa Rosa, 

California. 

Kelly, M. and R. Meentemeyer. 2002. Remote sensing of host species distribution in hardwood 

forests with sudden oak death in Marin and Sonoma Counties [abstract]. Page 26 in 

Proceedings of Sudden Oak Death, A Science Symposium, USDA Forest Service and 

University of California, Berkeley. 

Kinloch, B. B. 2003. White pine blister rust in North America: past and prognosis. 

Phytopathology 93:1044–47. 

Kliejunas, J. 2001. Sudden oak death, Phytophthora sp. Pest Risk Assessment. USDA Forest 

Service. 

Kliejunas, J. 2003. A Pest Risk Assessment for Phytophthora ramorum in North America. 

USDA Forest Service. 

Kliejunas, J. 2005. A Pest Risk Assessment for Phytophthora ramorum in North America. 

USDA Forest Service. 

Kluza, D. A., D. A. Vieglais, J. K. Andreasen, and A. T. Peterson. 2007. Sudden oak death: 

geographic risk estimates and predictions of origins. Plant Pathology 56:580–587. 

Kroon, L. P. N. M., E. C. P. Verstappen, L. F. F. Kox, W. G. Flier, and P. J. M. Bonants. 2004. 

A rapid diagnostic test to distinguish between American and European populations of 

Phytophthora ramorum. Phytopathology 94:613-620. 

76 
Lane, C. R., E. Hobben, L. Walker, V. C. Barton, A. J. Inman, K. J. D. Hughes, H. Swan, A. 

Colyer, and I. Barker. 2007. Evaluation of a rapid diagnostic field test kit for identification of 

a Phytophthora species, including P. ramorum and P. kernoviae at the point of inspection. 

Plant Pathology DOI: 10.1111/j.1365-3059.2007.01615.x. 

Levien, L., J. Mai, and W. Mark. 2002. Statewide aerial and ground surveys for mapping and 

monitoring the distribution of sudden oak death [abstract]. Page 27 in Proceedings of Sudden 

Oak Death, A Science Symposium, USDA Forest Service and University of California, 

Berkeley, 

Liebhold, A. M., W. L. MacDonald, D. Bergdahl, and V. C. Mastro. 1995. Invasion by exotic 

forest pests: a threat to forest ecosystems. Forest Science 41(2):1-49. 

Lilja, A., A. Rytkönen, M. Kokkola, P. Parikka, and J. Hantula. 2007. First Report of 

Phytophthora ramorum and P. inflata in Ornamental Rhododendrons in Finland. Disease 

Notes 91:1055. 

Linderman, R. G., and E. A. Davis. 2005. Survival of Phytophthora ramorum in potting mix 

components or soil and eradication with aerated steam treatment [abstract]. Phytopathology 

95:S61. 

Linderman, R. G., and E. A. Davis. 2006a. Survival of Phytophthora species and other pathogens 

in soilless media components or soil and their eradication with aerated steam. Pages 299-302 

in Frankel, S. J., P. J. Shea, and M. I. Haverty (tech. coor.). Proceedings of the Sudden Oak 

Death Second Science Symposium: The State of Our Knowledge. January 18-21, 2005, 

Monterey, CA. Gen. Tech. Report PSW-GTR-196. Albany, CA: Pacific Southwest Research 

Station, Forest Service, United States Department of Agriculture. 

Linderman, R.G., and E. A. Davis. 2006b. Evaluation of Chemical and Biological Agents for 

Control of Phytophthora species on Intact Plants or Detached Rhododendron Leaves. Pages 

265-268 in Frankel, S. J., P. J. Shea, and M. I. Haverty (tech. coor.). Proceedings of the 

Sudden Oak Death Second Science Symposium: The State of Our Knowledge. January 18-

21, 2005, Monterey, CA. Gen. Tech. Report PSW-GTR-196. Albany, CA: Pacific Southwest 

Research Station, Forest Service, United States Department of Agriculture. 

Linderman, R. G., and E. A. Davis. 2006c. Survival of Phytophthora ramorum compared to 

other Phytophthora species in potting medium components, compost and soil. 

HortTechnology 16:502-507. 

Linderman, R. G., and Davis, E. A. 2007a. Comparative host susceptibility and sporulation 

potential of Phytophthora ramorum on species, cultivars, and hybrids of camellia. Online. 

Plant Health Progress doi:10.1094/PHP-2007-0822-02-RS. 

Linderman, R. G., and Davis, E. A. 2007b. Evaluation of Phytophthora ramorum in nursery 

crop tissue culture propagation. Online. Plant Health Progress doi:10.1094/PHP-2007-

0822-01-RS. 

77 
Linderman, R. G., E. A. Davis, and J. L. Marlow. 2006. Response of selected nursery crop plants 

to inoculation with isolates of Phytophthora ramorum and other Phytophthora species. 

HortTechnology 16:216-224. 

Linderman, R. G., P. B. de Sá, and E. A. Davis. 2007. Comparative susceptibility of plants native 

to the Appalachian range of the United States to inoculation with Phytophthora ramorum. 

Online. Plant Health Progress doi:10.1094/PHP-2007-0917-01-RS. 

Magarey, R., L. Garrett, and G. Fowler. 2004. Risk Model for Phytophthora ramorum (Sudden 

Oak Death) in Nursery Shipments. Phytophthora ramorum Science Panel, Center for Plant 

Health Science and Technology, June 29-30, 2004, Raleigh, NC. 

Magarey, R. D., G. A. Fowler, D. M. Borchert, T. B. Sutton, M. Colunga-Garcia, and J. A. 

Simpson. 2007. NAPPFAST: An Internet System for the Weather-Based Mapping of Plant 

Pathogens. Plant Disease Vol. 91 No. 4. DOI: 10.1094/PDIS-91-4-0336. 

Magarey, R., G. Fowler, M. Colunga-Garcia, W. Smith, and R. Meentemeyer. 2008. (in press). 

Climate host mapping of Phytophthora ramorum, causal agent of sudden oak death. General 

Technical Report of the Third Sudden Oak Death Symposium. USDA Forest Service Pacific 

Southwest Research Station. 

Magnusson, C., B. Okland, and H. Solheim. 2001. Wood Chips. In: Risks of Exotic Forest Pests 

and Their Impact on Trade. An International Online Workshop to Reduce Movement of 

Forest Pests with a Minimal Impact on Trade. Last accessed January 13, 2005, from 

http://www.aspnet.org/online/ExoticPest/Index.html. 

Maloney, P. E., S. F. Kane, C. E. Jensen, and D. M Rizzo. 2002a. Epidemiology and ecology of 

Phytophthora ramorum in redwood/tanoak forest ecosystems of the California coast range 

[abstract]. Page 11 in Proceedings of Sudden Oak Death, A Science Symposium, USDA 

Forest Service and University of California, Berkeley. 

Maloney, P. E., D. M. Rizzo, S. T. Koike, T. Y Harnik, and M. Garbelotto. 2002b. First report of 

Phytophthora ramorum on coast redwood in California. Plant Disease 86:1274. 

Maloney, P. E., S. C. Lynch, S. F. Kane, and D. M. Rizzo. 2004. Disease progression of 

Phytophthora ramorum and Botryosphaeria dothidea on Pacific madrone. Plant Disease 88: 

852-857. 

Man in‘t Veld, W., H. de Gruyter, P. J. M. Bonants, and R. P. Baayen. 2002. Isozyme 

genotyping of Phytophthora ramorum reveals a remarkable homogeneity [abstract], Pages 

58-59 in Proceedings of the Sudden Oak Death, A Science Symposium, USDA Forest 

Service and University of California, Berkeley. 

Martin, F. N., and P. Tooley. 2001. Molecular phylogeny of Phytophthora based on 

mitochondrial gene sequences. American Phytopathology Society 91:S58. 

78 
Martin, F. N, P. W. Tooley, and R. Fredrick. 2002. The Use of mitochondrial molecular markers 

for identification of P. ramorum [abstract]. Page 18 in Proceedings of Sudden Oak Death, A 

Science Symposium, USDA Forest Service and University of California, Berkeley. 

Martin, F. N., P. W. Tooley, and C. Blomquist. 2004. Molecular detection of Phytophthora 

ramorum, the causal agent of Sudden Oak Death in California, and two additional species 

commonly recovered from diseased plant material. Phytopathology 94(6):621-631. 

McGregor, B. M. 1987. Tropical Products Transport Handbook (Agriculture Handbook No. 

668). United States Department of Agriculture, Washington, DC. 

McLaughlin, I., S. Jeffers, and T. Waldrop. 2007. Effects of prescribed burning on survival of 

Phytophthora cinnamomi in forest soil. Phytopathology 97:S74. 

Meentemeyer, R. and M. Kelly. 2002. Spacial modeling of sudden oak death risk and oak 

mortality clustering, China Camp State Park [abstract]. Page 25 in Proceedings of Sudden 

Oak Death, A Science Symposium, USDA Forest Service and University of California, 

Berkeley. 

Meentemeyer, R., D. Rizzo, W. Mark, E. Lotz. 2004. Mapping the risk of establishment and 

spread of sudden oak death in California. Forest Ecology and Management 200:195-214. 

Menge, J. A. and S. Nemec. 1997. Citrus. Pages 185-227 in R. J. Hillocks and J. M. Walker 

(eds.), Soilborne Diseases of Tropical Crops, CAB International, Wallingford. 

Meshriy, M., D. Hüberli, H. Tamar, L. Miles, K. Reuther, and M. Garbelotto. 2006. Variation in 

susceptibility of Umbellularia californica (bay laurel) to Phytophthora ramorum. Pages 87-

89 in S. J. Frankel, P. J. Shea, and M. I. Haverty (tech. coor.). Proceedings of the Sudden Oak 

Death Second Science Symposium: The State of Our Knowledge. January 18-21, 2005, 

Monterey, CA. Gen. Tech. Report PSW-GTR-196. Albany, CA: Pacific Southwest Research 

Station, Forest Service, United States Department of Agriculture. 

Monahan, W. B., and W. D Koenig. 2006. Estimating the potential effects of sudden oak death 

on oak-dependent birds. Biological Conservation 127:146-157. 

Moralejo, E., M. Puig, J. A. Garcia, and E. Descals. 2006. Stromata, sporangiomata and 

chlamydosori of Phytophthora ramorum on inoculated Mediterranean woody plants. 

Mycological Research 110:1323-1332. 

Murphy. S. K., and D. M. Rizzo. 2003. First report of Phytophthora ramorum on Canyon Live 

Oak in California. Plant Disease 87:315. 

Murphy, S. K., J. Bienapfl, D. M. Rizzo, Y. Valachovic, and C. Lee. 2006. Monitoring 

Phytophthora ramorum distribution in streams within Coastal California watersheds 

[abstract]. Page 531 in Sudden Oak Death Second Science Symposium: The State of our 

Knowledge. January 18-21, 2005, Monterey, California. 

79 
 

NAPPO. 2004. Glossary of Phytosanitary Terms, RSMP No. 5. North American Plant Protection 

Organization (NAPPO). Last accessed March 14, 2005, from 

http://www.nappo.org/Standards/REVIEW/RSPM5-e.pdf. 

NASS (USDA, National Agricultural Statistics Service). 2007. Floriculture and Nursery Crops 

Situation and Outlook Yearbook. United States Department of Agriculture. Economic 

Research Service FLO-2007. September, 2007. 

Oak, S., J. Hwang, S. Jeffers, and B. Tkacz. 2007. 2006 Pilot Survey for Phytophthora ramorum 

in Forest Streams in the USA. [abstract]. in Sudden Oak Death Science Symposium III. 

March 5-9, 2007, Santa Rosa, California. Last accessed November 1, 2007, from 

http://nature.berkeley.edu/comtf/sodsymposium/PDF/Abstracts/2006%20Pilot%20Survey%2 

0for%20Phytophthora%20ramorum%20in%20Forest%20Streams%20in%20the%20USAOak.pdf. 

OASS. 2004. Oregon Christmas Tree Survey – 2003. Oregon Agricultural Statistics Service 

(OASS). Last Accessed March 17, 2004, from 

http://www.nass.usda.gov/or/Christmastreerelease2003.pdf. 

ODA. 2001. Quarantine Regulation. Oregon Department of Agriculture (ODA). Last accessed 

April 1, 2005, from http://www.oda.state.or.us/plant/ppd/path/SOD/SOD_quar.html. 

ODA. 2007. Grower-assisted inspection program to help with sudden nursery demise. Oregon 

Department of Agriculture (ODA). News release, September 19, 2007. 

OSOS. 2004. Oregon Department of Agriculture Emergency Quarantine Order: Columbia 

County Nursery Stock, Potting Media and Compost. Oregon Bulletin, July 1, 2004. Oregon 

Secretary of State (OSOS). Last accessed March 17, 2005, from 

http://arcweb.sos.state.or.us/rules/0704_Bulletin/0704_othnotices_bulletin.html. 

OSOS. 2007a. Oregon Department of Agriculture Emergency Quarantine Order: Columbia 

County Nursery Stock, Potting Media and Compost. Oregon Bulletin, May 1, 2007. Oregon 

Secretary of State (OSOS). Last accessed November 1, 2007, from

 http://arcweb.sos.state.or.us/rules/0507_Bulletin/0507_ch603_bulletin.html. 

OSOS. 2007b. Updates Phytophthora ramorum quarantines: Adds newly detected sites in Curry 

County, new hosts, and protocols. Oregon Bulletin, November 1, 2007. Oregon Secretary of 

State (OSOS). Last accessed November 9, 2007, from

 http://arcweb.sos.state.or.us/rules/1107_Bulletin/1107_rulemaking_bulletin.html. 

Osterbauer, N. K. 2003. Phytophthora ramorum Werres, de Cock & Man in’t Veld. Pest risk 

assessment for Oregon. Last accessed December 3, 2004, from 

http://oda.state.or.us/plant/ppd/path/SOD/SOD_PRA_Oregon_2=03.pdf. 

Parke, J. L., and C. Lewis. 2007. Root and stem infection of rhododendron from potting medium 

infested with Phytophthora ramorum. Plant Disease 91:1265-1270. 

80 
Parke, J. L., E. M Hansen, and R. G. Linderman. 2002a. Sporulation potential of Phytophthora 

ramorum on leaf disks from selected hosts [abstract]. Page 33 in Proceedings of the Sudden 

Oak Death, A Science Symposium, USDA Forest Service and University of California, 

Berkeley. 

Parke, J. L., R. G. Linderman, and E. M. Hansen. 2002b. Assessing the susceptibility of Pacific 

Northwest nursery plants to Phytophthora ramorum using a detached leaf assay [abstract]. 

Pages 84-85 in Proceedings of the Sudden Oak Death, A Science Symposium, USDA Forest 

Service and University of California, Berkeley. 

Parke, J. L., R. G. Linderman, K. Hummer, and E. M. Hansen. 2002c. Differential susceptibility 

to Phytophthora ramorum among Vaccinium species and cultivars [abstract]. Pages 83-84 in 

Proceedings of the Sudden Oak Death, A Science Symposium, USDA Forest Service and 

University of California, Berkeley. 

Parke, J., J. Pscheidt, and R. Linderman. 2003. Phytophthora ramorum – A guide for Oregon 

nurseries. Dept. of Botany and Plant Pathology, Oregon State University Extension. EM 

8840. Last accessed March 22, 2005, from http://www.suddenoakdeath.org/. 

Parke, J. L., R. G. Linderman, N. Osterbauer, and J. A. Griesbach. 2004a. Detection of 

Phytophthora ramorum blight in Oregon nurseries and completion of Koch’s Postulates on 

Pieris, Rhododendron, Viburnum and Camellia. Plant Disease 88:87. 

Parke, J., J. Pscheidt, and R. Linderman. 2004b. Phytophthora ramorum – A guide for 

Washington nurseries. Dept. of Botany and Plant Pathology, Oregon State University 

Extension Service. Last accessed March 22, 2005, from http://www.suddenoakdeath.org/. 

Parke, J. L., M. L. Roth, and C. J. Choquette. 2006a. Detached leaf assays with Phytophthora 

ramorum: Are they valid? [abstract]. Page 535 in S. J. Frankel, P. J. Shea, and M. I. Haverty 

(tech. coor.). Proceedings of the Sudden Oak Death Second Science Symposium: The State 

of Our Knowledge. January 18-21, 2005, Monterey, CA. Gen. Tech. Report PSW-GTR-196. 

Albany, CA: Pacific Southwest Research Station, Forest Service, United States Department 

of Agriculture. 

Parke, J. L., M. L. Roth, and C. J. Choquette. 2006b. Phytophthora ramorum disease 

transmission from infested potting media [abstract]. Pages 291-293 in S. J. Frankel, P. J. 

Shea, and M. I. Haverty (tech. coor.). Proceedings of the Sudden Oak Death Second Science 

Symposium: The State of Our Knowledge. January 18-21, 2005, Monterey, CA. Gen. Tech. 

Report PSW-GTR-196. Albany, CA: Pacific Southwest Research Station, Forest Service, 

United States Department of Agriculture. 

Parke, J. L., E. Oh, S. Voelker, E. M. Hansen, G. Buckles, and B. Lachenbruch. 2007. 

Phytophthora ramorum colonizes tanoak xylem and is associated with reduced stem water 

transport. Phytopathology. 

81 
Pogoda, F., and S. Werres. 2002. Pathogenicity of European and American Phytophthora 

ramorum isolates to Rhododendron [abstract]. Page 85 in Proceedings of the Sudden Oak 

Death, A Science Symposium, USDA Forest Service and University of California, Berkeley. 

Pogoda, F., and S. Werres. 2004. Histological studies of Phytophthora ramorum in 

Rhododendron twigs. Can. J. Bot. 82:1481–1489. doi: 10.1139/B04-104. 

PPQ. 2007a. Pest ID 1.5. Plant Protection and Quarantine (PPQ), Animal and Plant Health 

Inspection Service, United States Department of Agriculture. Last accessed October 4, 

2007, from https://mokcs14.aphis.usda.gov/aqas/HomePageInit.do. 

PPQ. 2007b. Update on PPQ Diagnostics for SOD: Diagnostics procedures approved by APHIS 

and diagnostic analyses performed by APHIS PPQ for Phytophthora ramorum Revised 

6/5/07. Last accessed October 10, 2007, from http://www.aphis.usda.gov/plant_health/ 

plant_pest_info/pram/downloads/pdf_files/diagnosticssummary6-07.pdf. 

Prospero, S., E. M. Hansen, and L. M. Winton. 2005. Genetic uniformity of Phytophthora 

ramorum in North American forests revealed by microsatellite markers. Page 111 in Sudden 

Oak Death Second Science Symposium: The State of our Knowledge. January 18-21, 2005, 

Monterey, California. 

Prospero, S., E M. Hansen, N. J. Grünwald, and L. M. Winton. 2007. Population dynamics of 

the sudden oak death pathogen Phytophthora ramorum in Oregon from 2001 to 2004. 

Molecular Ecology 16:2958–2973. 

RAPRA. 2007. Distribution of Naturally Infected Hosts, Search in Database for Naturally 

Infected Hosts for Outdoor (not Nursery) listings in Germany, February 28, 2007. 

Distribution: Geographical Distribution Of Naturally Infected Hosts, Risk Analysis of 

Phytophthora ramorum (RAPRA), A project within the EU 6th Framework R & D 

Programme, priority 8.1.B.1 'Sustainable management of Europe's natural resources'. Last 

accessed February 28, 2007, from 

http://rapra.csl.gov.uk/objectives/wp1/naturalhostsearch.cfm. 

Rioux, D., B. Callan, and D. McKenney. 2006. Phytophthora ramorum: causal agent of sudden 

oak death, ramorum blight, ramorum bleeding canker, ramorum (shoot) dieback. Plant 

Health Risk Assessment. PRA# 00-39. Plant Health Risk Assessment Unit Science Division, 

Canadian Food Inspection Agency and Laurentian Forestry, Pacific Forestry and Great Lakes 

Forestry Centres, Canadian Forest Service. 

Ristaino, J. B., and M. L. Gumpertz. 2000. New frontiers in the study of dispersal and spatial 

analysis of epidemics caused by species in the genus Phytophthora. Annual Review of 

Phytopathology 38:541-76. 

Rizzo, D. M., M. Garbelotto, J. M. Davidson, G. W. Slaughter, and S. T. Koike. 2002a. 

Phytophthora ramorum and sudden oak death in California: I. Host relationships in R. 

Standiford and D. McCreary (eds.) 5th symposium on California Oak Woodlands. USDA 

Forest Service Gen. Tech. Rep. PSW-GTR-184. 

82 
Rizzo, D. M., M. Garbelotto, J. M. Davidson, G.W. Slaughter, and S.T. Koike. 2002b. 

Phytophthora ramorum as the cause of Extensive Mortality of Quercus spp. and Lithocarpus 

densiflorus in California. Plant Disease 86:205-214. 

Rizzo, D. M., and M. Garbelotto. 2003. Sudden Oak Death: endangering California and Oregon 

forest ecosystems. Frontiers in Ecology and the Environment 1(5):197-204. 

Rizzo, D. M., M. Garbelotto, and E. M. Hansen. 2005. Phytophthora ramorum: Integrative 

research and management of an emerging pathogen in California and Oregon forests. Annual 

Review Phytopathology 43:13.1-3.27. 

Rytkönen, A., A. Lilja, P. Parikka, A. Hannukkala, M. Kokkola, and J. Hantula. 2007. 

Phytophthora species in Finland. Page 62 in Meeting Abstracts of the Fourth International 

IUFRO Working Party 7.02.09, Phytophthoras in Forests and Natural Ecosystems. August 

26-31, 2007, Monterey, California. 

Schena, L., K. J. D. Hughes, and D. E. L. Cooke. 2006. Detection and quantification of 

Phytophthora ramorum, P. kernoviae, P. citricola and P. quercina in symptomatic leaves by 

multiplex real-time PCR. Molecular Plant Pathology 7(5):365-379. 

Schmidt, D., M. Garbelotto, D. Chambers, and S. Tjosvold. 2006. Effect of phosphonate 

treatments on sudden oak death in tanoak and Shreve’s oak [abstract]. Page 263 in S. J. 

Frankel, P. J. Shea, and M. I. Haverty (tech. coor.). Proceedings of the Sudden Oak Death 

Second Science Symposium: The State of Our Knowledge. January 18-21, 2005, Monterey, 

CA. Gen. Tech. Report PSW-GTR-196. Albany, CA: Pacific Southwest Research Station, 

Forest Service, United States Department of Agriculture. 

Schwingle, B. W., J. A. Smith, and R. A. Blanchette. 2007. Phytophthora species associated 

with diseased woody ornamentals in Minnesota nurseries. Plant Disease 91:97-102. 

Shaw, C. G., and J. M. Davidson. 2003. Pathways of movement for Phytophthora ramorum, the 

causal agent of Sudden Oak Death. Sudden Oak Death Online Symposium. The American 

Phytopathological Society. Last accessed October 15, 2007, from 

http://www.apsnet.org/online/SOD/Papers/Shaw_Davidson/default.htm. 

Shelly, J, W. Tietje, and D. McCreary. 1996. Resource Evaluation for Forest Products. Chapter 

8. IN Guidelines for Managing California’s Hardwood Rangelands. University of California 

Division of Agriculture and Natural Resources Publication 3368. Oakland, CA. 

Shelly, J., R. Singh, C. Langford, and T. Mason. 2005a. Evaluating the survival of Phytophthora 

ramorum in firewood. [abstract]. Page 112 in S. J. Frankel, P. J. Shea, and M. I. Haverty 

(tech. coor.). Proceedings of the Sudden Oak Death Second Science Symposium: The State 

of Our Knowledge. January 18-21, 2005, Monterey, CA. Gen. Tech. Report PSW-GTR-196. 

Albany, CA: Pacific Southwest Research Station, Forest Service, United States Department 

of Agriculture. 

83 
Shelly, J., R., Singh, C. Langford, and T. Mason. 2005b. Understanding the disposal and 

utilization options for sudden oak death – diseased wood [abstract]. Page 86 in S. J. Frankel, 

P. J. Shea, and M. I. Haverty (tech. coor.). Proceedings of the Sudden Oak Death Second 

Science Symposium: The State of Our Knowledge. January 18-21, 2005, Monterey, CA. 

Gen. Tech. Report PSW-GTR-196. Albany, CA: Pacific Southwest Research Station, Forest 

Service, United States Department of Agriculture. 

Shishkoff, N. 2006. Susceptibility of Camellia to Phytophthora ramorum. Plant Health 

Progress doi:10.1094/PHP-2006-0315-01-RS. Last accessed August 27, 2007 from 

http://www.plantmanagementnetwork.org/pub/php/research/2006/camellia/Pramorum.pdf. 

Shishkoff, N. 2007. Persistence of Phytophthora ramorum in soil mix and roots of nursery 

ornamentals. Plant Disease 91:1245-1249. 

Shishkoff, N. 2007b. Susceptibility of some Lilac cultivars and other members of the Oleaceae to 

Phytophthora ramorum. Online. Plant Health Progress doi:10.1094/PHP-2007- 1101-02-RS. 

Last accessed January 15, 2008 from 

http://www.plantmanagementnetwork.org/sub/php/research/2007/Lilac/Lilac.pdf. 

Shishkoff, N. and P. Tooley. 2004. Persistence of Phytophthora ramorum in nursery plants and 

soil. Phytopathology 94:S95. 

Shurtleff, M. C. , and C. W. Averre. 1997. Glossary of Plant-Pathological Terms. APS Press, 

The American Phytopathology Society, St. Paul, MN. 

Smart, C.D., and W. Fry. 2001. Invasions by the late blight pathogen: renewed sex and 

enhanced fitness. Biological Invasions 3:235–243. 

Smith, W. D., E. M. Goheen, F. Sapio, K. W. Gottschalk, S. Frankel, and P. Dunn. 2002. 

Development of a National Survey Protocol for Detection of Phytophthora ramorum 

[abstract]. Page 24 in Proceedings of the Sudden Oak Death, A Science Symposium, USDA 

Forest Service and University of California, Berkeley. 

Standiford, R. B. 2000. California’s hardwood rangelands: production and conservation values. 

University of California Cooperative Extension Oak Fact Sheets No. 89. 

Steeghs, M. H. C. G. 2008 (In press). Contingency planning for Phytophthora ramorum 

outbreaks: Progress report Work Package 7, EU RAPRA Project. Sudden Oak Death 

Symposium III. March 5-9, 2007, Santa Rosa, California. 

Stipes, R. J., and R. J. Campana (eds.). 1981. Compendium of Elm Diseases. APS Press, St. 

Paul. 

Storer, A. J., K. E. Keirnan, N. K. Palkovsky, B. W. Hagen, G. W. Slaughter, N. M. Kelly, and 

P. Svihra. 2002. Sudden Oak Death: Diagnosis and Management. University of California, 

Cooperative Extension in Marin County. Pest Alert #6:1-12. 

84 
Suslow K. 2008 (in press). Determing the effectiveness of the Federal Order/Interim Rule on 

Phytophthora ramorum dissemination in nurseries. Proceedings of the Sudden Oak Death 

Symposium III. March 5-9, 2007, Santa Rosa, California. 

Suslow, K., K. Kosta, G. Raabe, and S. Cohen. 2005. Best Management Practices for the 

California Nursery Industry for Sudden Oak Death (SOD) Biosecurity (Revised 10-20-03; 

K. Suslow, K. Kosta, G. Raabe, S. Cohen) (Draft Revision 5-05 K. Suslow). Nursery 

Committee of the California Oak Mortality Task Force. Last accessed October 15, 2007, 

from http://www.suddenoakdeath.org/pdf/NurseryBMPs5.04.pdf. 

Swain, S., T. Harnick, M. Mejia-Chang, J. Creque, and M. Garbelotto. 2002. Survivability of 

Phytophthora ramorum in the composting process [abstract]. Page 44 in Proceedings of 

Sudden Oak Death, A Science Symposium, USDA Forest Service and University of 

California, Berkeley. 

Swain, S., and M. Garbelotto. 2006. Potential for re-infection of finished compost by 

Phytophthora ramorum [abstract]. Pages 483-486 in S. J. Frankel, P. J. Shea, and M. I. 

Haverty (tech. coor.). Proceedings of the Sudden Oak Death Second Science Symposium: 

The State of Our Knowledge. January 18-21, 2005, Monterey, CA. Gen. Tech. Report PSWGTR-196. Albany, CA: Pacific Southwest Research Station, Forest Service, United States 

Department of Agriculture. 

Swain, S., T. Harnick, M. Mejia-Chang, K. Hayden, W. Bakx, J. Creque, and M. Garbelotto. 

2005. Heat and composing effects of the viability of Phytophthora ramorum, when grown on 

a variety of artificial and plant substrates. Final Report. University of California, Berkeley. 

http://www.cnr.berkeley.edu/garbelotto/downloads/compostreport05.pdf. 

Swain, S., T. Harnik, M. Mejia-Chang, K. Hayden, W. Bakx, J. Creque, and M. Garbelotto. 

2006. Composting is an effective treatment option for sanitization of Phytophthora ramoruminfected plant material. Journal of Applied Microbiology 101:815-827. 

Swiecki, T. J., and E. A. Bernhardt. 2002a. Factors related to Phytophthora canker (sudden oak 

death) disease risk and disease progress in coast live oak and tanoak. Report for USDA 

Forest Service, Phytosphere Research Project No. 2001-0802, July 28, 2002. 

Swiecki, T. J., and E. A. Bernhardt. 2002b. Evaluation of stem water potential and other tree and 

stand variables as risk factors for Phytophthora ramorum canker development in coast live 

oak. in R. Standiford and D. McCreary (eds.) 5th Symposium on California Oak Woodlands. 

USDA Forest Service, Gen. Tech. Rep. PSW-GTR-184. 

Thomas, J. D. 1997. California’s oak woodlands: where we have been, where we are, where we 

need to go. Pages 3-9 in N. H. Pillsbury, J. Verner, and W. D. Tietje (technical coordinators). 

Proceedings of a symposium on oak woodlands: ecology, management, and urban interface 

issues; 19-22 March 1996; San Luis Obispo, CA. USDA Forest Service, Pacific Southwest 

Research Station, General Technical Report PSW-GTR-160. Albany, CA. 

85 
Titko, S. 2003. Potential for mitigation of P. ramorum in wood and bark through mulch piles. 

Personal communication to B. Randall-Schadel from Steve Titko (Growing Media Business 

Group, Scotts Company) as captured in email to D. Kaplan on January 8, 2003. Archived in 

PERAL Library, Raleigh, NC. 

Tjosvold, S. A., D. L. Chambers, J. Tse, J. M. Davidson, M. Garbelotto, and D. M. Rizzo. 2002a. 

Evaluation of a novel diagnostic procedure to detect the presence of Phytophthora ramorum 

by sampling ooze from infected cankers [abstract]. Pages 91-92 in Proceedings of Sudden 

Oak Death, A Science Symposium, USDA Forest Service and University of California, 

Berkeley. 

Tjosvold, S. A., D. L. Chambers, J. M. Davidson, and D. M. Rizzo. 2002b. Incidence of 

Phytophthora ramorum Inoculum Found in Soil Collected from a Hiking Trail and Hikers’ 

Shoes in a California Park [abstract]. Page 53 in Proceedings of Sudden Oak Death, A 

Science Symposium, USDA Forest Service and University of California, Berkeley. 

Tjosvold, S. A., D. L. Chambers, J. M. Davidson, and D. M. Rizzo. 2002c. Incidence of 

Phytophthora ramorum Inoculum Found in Streams Running through Areas of High 

Incidence of Sudden Oak Death in Santa Cruz County [abstract]. Pages 52-53 in Proceedings 

of Sudden Oak Death, A Science Symposium, USDA Forest Service and University of 

California, Berkeley. 

Tjosvold, S. A., K. R. Buermeyer, C. Blomquist, and S. Frankel. 2004. Guide to Diseases of 

Phytophthora ramorum in Ornamental Nurseries, Diagnosis and Management. Draft, 

October 2004. Last accessed March 22, 2005, from http://www.suddenoakdeath.org. 

Tjosvold, S. A., D. L. Chambers, and S. T. Koike. 2006a. Evaluation of fungicides for the 

control of Phytophthora ramorum infecting Rhododendron, Camellia, Viburnum and Pieris 

[abstract]. Pages 269-271 in S. J. Frankel, P. J. Shea, and M. I. Haverty (tech. coor.). 

Proceedings of the Sudden Oak Death Second Science Symposium: The State of Our 

Knowledge. January 18-21, 2005, Monterey, CA. Gen. Tech. Report PSW-GTR-196. 

Albany, CA: Pacific Southwest Research Station, Forest Service, United States Department 

of Agriculture. 

Tjosvold, S. A., D. L. Chambers, S. L. Thomas, and C. L. Blomquist. 2006b. First Report of 

Phytophthora ramorum infecting Camellia flower buds in North America. Online. Plant 

Health Progress doi:10.1094/PHP-2006-0825-01-BR. 

Tooley, P. W., and K. L. Kyde. 2003. Susceptibility of some eastern oak species to sudden oak 

death caused by Phytophthora ramorum. [Abstract]. Phytopathology 93:S84. Publication no. 

P-2003-0614-AMA. 

Tooley, P. W., and K. L. Kyde. 2007. Susceptibility of some eastern forest species to 

Phytophthora ramorum. Plant Disease 91:435-438. 

86 
Tooley, P. W., K. L. Kyde, and L. Englander. 2004. Susceptibility of selected Ericaceous 

ornamental host species to Phytophthora ramorum. Plant Disease 88:993-999. 

Tubajika, K., R. Singh, and J. Shelly. 2008 (in press). The efficacy of heat treatment to control 

Phytophthora ramorum in infected wood species. Proceedings of the Sudden Oak Death 

Symposium III. March 5-9, 2007, Santa Rosa, California. 

Tubajika, K. M., J. J. Jonawiak, R. Mack and K. Hoover. 2006. Efficacy of radio frequency 

treatment and its potential for control of sapstain and wood decay fungi on red oak, poplar, 

and southern yellow pine wood species. Journal of Wood Science 53:258–263 (DOI 

10.1007/s10086-006-0844-x). 

Turner, J., P. Jennings, S. McDonough, D. Liddell, and J. Stonehouse. 2006. Chemical control of 

Phytophthora ramorum causing foliar disease in hardy nursery stock in the UK. [abstract], 

Pages 273-174 in S. J. Frankel, P. J. Shea, and M. I. Haverty (tech. coor.). Proceedings of 

the Sudden Oak Death Second Science Symposium: The State of Our Knowledge. January 

18-21, 2005, Monterey, CA. Gen. Tech. Report PSW-GTR-196. Albany, CA: Pacific 

Southwest Research Station, Forest Service, United States Department of Agriculture. 

USBC. 1998. Statistical Abstract of the United States 1996. 200th ed. Washington, DC: U.S. 

Bureau of the Census, U.S. Government Printing Office. 

USDA. 2003. USDA Plant Hardiness Zone Map. USDA Miscellaneous Publication No. 1475, 

Issued January 1990. http://www.usna.usda.gov/Hardzone/ushzmap.html. 

USFWS. 2007. Endangered and Threatened Plants. U.S. Fish and Wildlife Service. 

Last accessed October 17, 2007, from http://a257.g.akamaitech.net/7/257/2422/ 

09nov20051500/edocket.access.gpo.gov/cfr_2005/octqtr/pdf/50cfr17.12.pdf 

USITC. 2005. Interactive Tariff and Trade Dataweb. United States International Trade 

Commission. Last accessed February 10, 2005, from http://dataweb.usitc.gov. 

Van der Plank, J. E. 1963. Plant Diseases: Epidemics and Control. Academic Press, New York. 

Vettraino, A. M., B. Ceccarelli, and A. Vannini. 2007. Potential risk of spread of Phytophthora 

ramorum in Mediterranean wild environments and nurseries [abstract]. Page 28 in 4th IUFRO 

Phytophthoras in Forests & Natural Ecosystems, Meeting Abstracts, August 26-31, 2007. 

Von Broembsen, S. 1999. Disease management for nurseries using recycling irrigation systems. 

Last accessed March 28, 2005, from http://entoplp.okstate.edu/zoospore/index.html. 

Webber, J. F., and J. Rose. 2008 (in press). Dissemination of aerial and root infecting 

Phytophthoras by human vectors [abstract]. Pages 275-278 in Proceedings of the Sudden 

Oak Death Symposium III. March 5-9, 2007, Santa Rosa, California. 

87 
Werres, S., and D. De Merlier. 2003. First detection of Phytophthora ramorum mating type A2 

in Europe. Plant Disease 87:1266. 

Werres, S., and B. Ziekle. 2003. First studies on the pairing of Phytophthora ramorum. 

Zietschrift für Plfanzenkrankheiten und Plfanzenschutz 110(2):120-130. 

Werres, S., R. Marwitz, W. A. Man in‘t Veld, A. W. A. M. De Cock, P. J. M. Bonants, M. De 

Weerdt, K. Themann, E. Ilieva, and R. P. Baayen. 2001. Phytophthora ramorum sp. nov., a 

new pathogen on Rhododendron and Viburnum. Mycological Research 105:1155-1165. 

Werres, S., Wagner, S., Brand, T., Kaminski, K., and D. Seipp. 2007. Survival of Phytophthora 

ramorum in recirculating irrigation water and subsequent infection of Rhododendron and 

Viburnum. Plant Disease 91:1034-1044. 

Widmer, T. L. 2007. Investigating the potential of biological control against Phytophthora 

ramorum [poster]. Sudden Oak Death Symposium III. March 5-9, 2007, Santa Rosa, 

California. Last accessed January 15, 2008, from 

http://nature.berkeley.edu/comtf/sodsymposium/PDF/Posters/Investigating%20the%20Potent 

ial%20of%20Biological%20Control%20against%20Phytophthora%20ramorum-Widmer.pdf 

Wilhelm, S., and A. O. Paulus. 1980. How soil fumigation benefits the California strawberry 

industries. Plant Disease 64:264-270. 

Winton, L. M., and E. M. Hansen. 2001. Molecular diagnosis of Phytophthora lateralis in trees, 

water, and foliage baits using multiplex polymerase chain reaction. Forest Pathology 31:275-

283. 

Zielke, B., and S. Werres. 2002. Taxonomic investigations of European and American isolates of 

Phytophthora ramorum [abstract]. Pages 59-60 in Proceedings of Sudden Oak Death, A 

Science Symposium, USDA Forest Service and University of California, Berkeley. 

88